a question on footprint, another on scale

Hello -
Planning my first grow and had a few questions I was hoping folks could weigh-in on:

Would the tent size - 2x4, 4x4, etc. - be the total footprint, or should I account for a bit of room mourned the tent? Due to space constraints, looks as though I may need to run two tents side by side, with both tents flush against at least one wall.

Apart from the light(s), is there much of a cost jump between a 2x4 and a 4x4 set-up, or a 4x4 and a 5x5? I can appreciate a 8" fan will probably cost more than a 6", but it seems like the overall cost difference - again, excluding the light - would be minimal (<$1k?).

Initially I was thinking of setting up in my garage, but am now looking at a 2x7x8 space in my office; 2x2 for veg and 2x4 for flower.

Appreciate any input/comments; thank you -

The price can be a little more for the lighting to do 5x5 area over 2x4 area but the air exchange fans and whatever else your using should be around the same prices give or take a few dollars and as far as the footprint that depends on you and what your comfortable with you could easily fill a 4x4 wall to wall and still work it

thank you for the info!