you can get buy with 2 clamped at opposite ends. if you have a glass versatop, you might be able to use 4 smaller sized ones. i used 3 6.5" domes over my 20g high.
stick with the 6500k and skip the 5000k as they are too yellow and benefit our viewing more than plant growth. If you really want the plant colors to pop, add some red grow bulbs. They are available through hydroponic outlets or online.
"I am Groot", the faithful protector