I'm sort of getting the hang of setting up tanks quickly, so here's my checklist:
- filter, because trust me, anything above three gallons is REALLY ANNOYING to do 50 and 100% water changes on. This'll enable you to do a fish-in cycle.
- water conditioner
- silk plants, or real plants if you're up for that! A good rule of thumb for silk plants is that you should be able to run a nylon against them and not have it tear. They should be specifically labelled as silk.
- gravel/substrate is only mandatory if you want live plants. I have a few bare-bottom tanks and a few with gravel, and a couple that just have coloured stones scattered around the bottom-- it's up to you!
- a hidey-place or two. If you can't find any caves/hidey-holes in the petstore that you like, or that seem smooth enough, new never-been-in-the-dishwasher coffee mugs or terra cotta pots work well!
Also useful to have:
- water test kit-- with vials, not strips, usually about $35 (this'll be for the cycle, and they last forever so you can use it on future tanks too!)
- a 1 gallon bucket/bowl/somethingorother that hasn't been used for anything else, which you can use for water changes.
In terms of your lid, if you're worried about jumping, you can just opt to keep the water level down a couple of inches from the black rim to discourage it too.
Also: welcome! :) I'd love to see pictures of your new betta once you pick one out.