Here’s a list of supplies to check off:

• Tank (10 gallon would be easiest to maintain, especially good for an office where you’re not there all the time to monitor, and more water volume + more plants and one betta means less water changes in the long run)
• Filter (I like HOBs personally, saves space in the tank - and quiet up nicely over time)
• Heater (50watt adjustable would work great for 5-10gal)
• Substrate
• Decorations/plants
• Water conditioner
• Gravel vacuum for water changes
• 2 Buckets for water changes
• Thermometer
• Food
• Test kit
• Ammonia (pure ammonia, Dr. Timms is good if you have it but if not then you can also use fish food or cleaning ammonia with no additives)
• Sponge, biomedia

Here’s info on fishless cycling which should be completed before getting the fish for smooth sailing:

Info:

• Nitrogen Cycle
• Fishless Cycling Guide
• Cycle Diagram

Supplies:

• Seachem Prime
  
• API Master test kit
• Ammonia source

Tips related to cycling/the cycle:

• Keep temp closer to 80°F/26.5°C
• After your tank is cycled perform weekly water changes between 25-50%, avoid doing more than 50% to maintain balance of tank’s cycle.
• Swish/squeeze filter media in old tank water during a water change once a month to get gunk off, never replace or rinse in tap water as it may crash your cycle
• Carbon in the filter is pretty useless usually, its good for pulling medicine out of the water if needed but it’s not necessary in a cycled betta tank - if your filter comes with this you can set it aside and use foam and biomedia instead!
• You can buy supplemental bacteria to speed up the cycling process, shake the bottle vigorously and add as much as you want in! Tetra Safestart Plus and Seachem Stability are two good ones.
• When gravel vacuuming it’s most efficient to crimp the tube so you get most of the dirt but don’t take too much water out (Here’s a how-to: https://youtu.be/LYv5n0a85OY)
• Filter Media Cheat Sheet