You can make your own dividers, there's a lot of the topics floating around here for making them so you can search that by yourself. :)
You should cycle the tank, you could do a in fish cycle with Cho'Gath, because it would better for him, better than living in that 0.5g.
Make sure your tank is heated, grab some nice food, people recommend NLS and OO here, Atison's if you can find it.
Decorate however you like to~ You can use sand, or gravel for substrate, or even go bare and not have any substrate. Silk plants are cheap and nice for decorations, if you wanna do live plants you'll have to research a bit in that area, we have sub-forum for that. :)
Hehe, you should get a purple Betta and call him Malzahar. ;)