I would use the bigger pots for sweet. I have grown all three varieties. The thai and genovese are more bushy. Personally, I love sweet basil. If you are new to basil..don't forget to cut all the first flowers off. Basil loves to be pruned and will thank you with a fresh new tastier and bushier plants. Also, make some tomato basil salad and pesto. Yummy! I have Sweet, purple and lettuce leaf this year. I will update on recipes and growth in my blog section. FYI: you may want to label those pretty herbs...www.nickiadkins.com

Here is a link that might be useful: www.nickiadkins.com

Hi, I grew 3 massive sweet basil last year on my balcony in a file box. I let one go to seed and hacked it down and ate it...that left me with 2 massive sweet basils. I grew these in a box that is barely bigger than the common manilla file., slightly taller but not much wider. I would say it used about 4 gal of dirt; tops.It was also rectangular.. lots of room to freely spread without running into the neighbor too much.
I used quite a bit of compost a third to almost almost half, then i also used potting mix from my garden shop ( black gold) and perlite and rock bits mixed in real good for drainage... I drilled several holes on the bottom and a few on the side near the bottom for rain drainage and overflow control... and also grew a bit of thyme in there that did real well untill it got too much shade from the basils.It billowed over the edge and came back to abundance. I planted my basil at about 8 inches tall with 2 or 3 really good sets of leaves, I pinched it all the time, hacked off peices for recipes all summer... It grew in that dumb file box to over 4 feet -not in bolt. In bolt it was over my head.( i am short though). I am doing the same this year. It was delicious. I think the rectangular shape of the box did wonders for them.

My sweet basil is about as big as a determinate tomato right now. Two feet high, eighteen inches wide. It's pretty early in the season and I pick two handfuls at least every other day.
I give it fish emulsion/seaweed fertilizer, it's in composted horse manure a full sun. I would go less than 5 gallons with the sweet and genovese. The Thai is smaller, a three gallon should work.

Hi. Would the 5 gallon pot hold only 1 basil plant or can I add a couple more?

It will probably do better if you only put one plant in a pot that size.

That said, when I start it from seed, I've had basil get ginormous in 4" "temporary" pots. So if you put a couple in a 5 gallon container, I doubt either one will die.