Fitting 6 plants in a smaller tent

I would get another tent and light I would only do 3 max in the space you have

I am sure there are many growers that would put 9 plants in a tent that size and not think twice about it. They would veg sooner producing a higher volume of smaller plants to maximize yield in the shortest possible time. I tend grow fewer but larger plants. I've had one plant completely fill a 3x3 tent and I've had four plants in the same space. In your situation I'd put the six plants in together and determine the switch to flowering by how large they are getting. As for your pot sizes. The smallest I use is 19L (5 gallon) but I normally go even bigger. If you are using 8-15 liter pots then I'd definetely put all six plants in the same tent. Those are tiny pots so you'll want to keep the plants smaller. You might only be 4 or 5 weeks from planting/sprouting to switching to flower.

I have a 3’x3’x6’ tent and two autoflowers had it almost full, unless you’re a fairly experienced grower I wouldn’t over crowd a grow space as it can be very overwhelming

Your plants will get bigger and go over the sides of potters. Need to plant plants based on size they get flowering and your grow skill and type of growing. Plus length of grow if doing photoperiods. So if you are really close to one another now then you will need more room. Good luck and happy growing 🌱