So, I usually recommend, especially for beginners, to do your first all male peacock/hap tank in a 75 footprint tank. It gives you a lot more stocking options because it allows you to select some of the more docile but larger haps, allows for more territory, and gives a little more swimming room. A 55 footprint (like your 60 gallon) is going to be tougher to stock (just too many conspecifics) and tougher to keep all your fish colored up (which is sort of the point of an all male tank).
Other than that basic advice I'll try to itemize things to match your list. Obviously, if you have more questions, don't hesitate to ask.
-Sand substrate
That's the right choice, I also always nudge people to go towards a calcium based sand like Ecco Complete or Estes Marine. You will always have algae in an African Cichlid tank, but with calcium based sand you're more likely to get pretty green algae instead of the ugly browns and reds of diatoms you'll get from silica based sand.
-Limestone rock used to create various hideaways
Unlike mbuna, rockwork doesn't necessarily have to be to create caves/hiding spots--but you do want pass throughs (little 'tunnels' that a fish can swim through to lose a chasing fish), and sight blocks (tall things that can be swum behind to break eye contact).
-canister filter: https://www.amazon.com/dp/B0002DJ9NY?ref=yo_pop_ma_swf
Not enough filtration for a 60 gallon African Cichlid tank. That's an okay filter (i'm not a huge PennPlax guy, but apart from Eheim and Fluval which are the best made cans, it's really about personal preference). If you like that filter at that price point (which is pretty cheap) you'll want two on your tank.
-factory lights, basic air pump/stone, and an aqueon submersible heater.
If you are going to run an air pump, then have it drive a sponge or internal filter. Bubbles offer very little to the tank on their own. Heater is some place you never want to skimp as it's the thing that can wipe your tank by failing. For a glass bodied heater I recommend the Eheim Jagers. Super reliable and an accurate thermostat. I also personally always try to push for people to not settle for stock lighting, especially with an all male, a good light will bring out colors that a bad light will never let you see. It's a place you can save money initially, but an investment that you'll never regret. I also recommend painting the back of the tank--i like a flat or eggshell black, some people like a blue, and other people dig the posters of backgrounds. Having it covered by any will improve the look of your tank and keep your fish a little less stressed.
-It's best to introduce as juveniles.
It is easiest to introduce as juvies as it lets you get to know your fish's personality and reduce introduction aggression. You can introduce adults pretty easily if done correctly, though.
We have capacity for 8-10 peacock cichlids.
Depending on the size of your fish 8-12 is a pretty safe range for all male peacock/hap.
Plants not necessary, sometimes these fish may uproot/destroy plants. If we do add plants they should be hearty.
Peacocks/Haps aren't as 'diggy' as mbuna, but they can still do it while nest prepping (something they do even in an all male), if you want plants, pick things that don't need to be planted but can be tied like Anubias, Java fern, and Java Moss.
-pH levels should be 7.5-8.5.
That's probably the maximum range, the ideal range is probably closer to 7.8-8.2.
-temp between 76-80
You can even go a little warmer, 76-82
-Dietary suggestions: brine shrimp, bloodworms, green veggies, pellets
Pick a single high quality pellet and stick with it. Northfin, Dainichi, NLS are all good choices if you're in north america. I feed 1mm sinking even to adulthood with 6-7" fish. You can add a small amount of high quality flake to your normal feeding routine if you have really, really shy eaters--but honestly, it's best to pull out super shy fish in a 55 footprint all-male.
-Avoid: eureka red, lwanda, yellow jake Jacobfreibergis, OB's, Dragonbloods.
Some of those are a little more aggressive, but they aren't deal breakers unless you're stocking a ton of super docile peacocks. Also, if you cut out all of them you're going to have a really hard time getting 8-10 non-conspecifics. And in fairness Stus (*A. stuartgranti) can be tough customers as well. When picking a stock list, you'll need to have alternates!
-How big of a temporary quarantine tank should I set up to have on hand as i may need when introduce or if I need to remove a problem fish?
A 20 gallon long with dividers will allow you to quarantine 2-3 fish at once, however, if they're coming from different sources it means you risk cross contamination. Personally I'd have a 20 long and a 10 gallon. If there's nothing in them keep the filter media in with your canister media (or just run extra sponge filters in the main tank).
-Where to purchase the fish, I live in St Louis but am willing/able to buy online if anyone can recommend a reputable store/website?
I always recommend Dave's Rare Aquarium Fish, for any and all African cichlid needs. He ships via Southwest Airlines, so as long as they fly to an airport near you it's essentially 12 hour delivery or less. Live Fish Direct, Bluegrass Aquatics, and Imperial Tropicals all have some ups and downs but some really good lines as well.
-Can anyone recommend a variety of 8-10 different peacock cichlids ( or other cichlids too) that would work in a tank together? Could also include cichlids that aren't peacock but still compatible.
So the short answer is sure, but the best way to do this is for you to pick 3-4 fish that are 'must haves' and let us build a stock list around that with alternates choices. We need to have some idea of what you're looking for.
Once my tank is cycled how many fish should I introduce at one time? How long to wait before introducing new fish?
Best way to do it is to have a hardy fishless cycle for 2-3 ppm of ammonia in 24 hours, and then to buy all your fish from the same source and introduce them all at once. Your best bet to ensure you get a male of each species is 3 juvies for each species, and scoop out females and sub dominant males and take them to a LFS for donation.
-Any meds/items I should have on hand other than seachem prime/paraguard?
I prefer Metronidazole to paraguard, though they don't always treat the same things. I recommend at least an API Freshwater Master Test kit as well is the GH/KH test. Have you tested your water out of the tap? If you need to buffer have you decided if you're going proprietary salt blends or the poor man's method? I always recommend getting a bottle of Trace Elements for African Cichlids (Kent and Seachem both make a good product), as well as something like VitaChem which allows you to add some extra vitamins--but if you have a good pellet that's more a luxury than a necessity.
Anything I am overlooking???
Don't spend the money on a crappy black plastic lid. It's a little more up front but a glass lid allows for less evaporation and is much easier to clean. A magfloat algae scraper is worth it's weight in gold. Make sure to get two nets, and the black ones seem to work better for catching fish.
But the number one thing for a cichlid tank for me is a Python No Spill fill and drain kit. Africans make a lot more waste than standard tropicals so you're going to need to do more and larger water changes. This beats lugging buckets!
I have two Penn Place Cascade Cannisters 1000s. https://www.amazon.com/dp/B0002DJ9NY?ref=yo_pop_ma_swf
After going through my fair share of filters I would definitely recommend a canister filter. Fluval is the more popular brand but I found the Penn-Plax is a better bang for your buck:
Also, Petco carries them and they may price match it for you. Technically they say they won't price match with amazon but I've had luck with them price matching amazon more often than not. I'd recommend getting a size larger than what your tank is. It'll keep your tank extra clean and you can continue to use it when you're forced to get an even larger tank.