I have a 1-2 x 1.2m (1.44m3)
and a 2.4 x 1.2 (2.88m3)
In the 2.88m3 I get 18 plants in 18lt pots
(2 x Wilma BIG 9 systems).
It would be helpful if you posted the exact dimensions of the space,
Is it 1 x 6m 9 or 2 x 3m ????
If it is quite square you'll need a walkway down the middle - or you'll not be able to reach half the plants.
Even in my 1.2 x 1.2 getting the plants at the back isn't easy.
If you're a beginner - which I assume you are, from the nature of your questions, I would STRONGLY RECOMMEND you starting with a MUCH SMALLER area.
Double up on size (and wattage) every crop BUT START SMALL.
There's a lot more to this than you'd believe - And a lot of very different things that can go wrong.
Start with 1.2 x 1.2m, a 600w (or a 1000w dimmable used on the 600w seting - you can increase later)
9 plants and LEARN THE CRAFT IN A MANAGABLE GARDEN