I've been using this flash since early Decemeber 2014. I do Real Estate photography, and I shoot 3-4 homes a day, 5 days a week. So I use this flash HUNDREDS of times a week, and it's been fantastic. http://www.amazon.com/Yongnuo-Professional-Speedlight-Flashlight-Olympus/dp/B00BXA7N6A/ref=sr_1_1?ie=UTF8&qid=1444003750&sr=8-1&keywords=yongnuo+yn560+iii
am no pro so YMMV but I feel 90% confident saying
if you're going 'manual' then yes, all basic flashes work with your hot shoe
a basic setup (I would suggest the Yungnuo line, myself) would be a fine intro and all that softbox stuff is compatible with all the 'standard' full-size flashes you may consider.
you can buy some very cheap flash diffusers so it's a great way to jump in and play around without much risk.