Lots of ways to look at this. If you are pretty content growing 1 or two plants, a 3x3 would plenty of space. And you can can get a very nice setup in 3x3 for about the same cost of a bare bones 4x4. With a little experience you can grow several small plants in a 3x3, there are members here that do it very well. A lot of people prefer the bigger space because it provides a little more room to work. But it’s also more room to have to reach into/lean, bend, or reach in most cases. As to where the typical 3x3 you can reach all corners from a single access point a little easier. So put some thought into those things.
You could look at seeds the same way. If you’re worried about cost effectiveness, 1-2 is a great idea for reasons stated above. If you screw up big time you will have plenty more. But if you started something like 4 plants you would have less veg time to a fuller canopy. You can look at that as more yield in your space on less time. The other advantage to starting more plants is that if one has issues you don’t lose your whole grow if you lose the plant.
If there’s not a physical handicap involved that justifies the bigger grow space, I think there is a good amount of value in doing a little smaller space well as opposed to trying to outfit larger space on same budget.