I'm in a similar place right now. I've finally negotiated my parents into letting me get a TIG welder, and setting up a shop space once and for all (that space is MY space to manage and worry about, so long as it doesn't endanger anyone or the house, meaning I can pack as many machines as I want into it, so long as it's safe). I have a few basic ideas for my layout, which is in a space that'll be about 25'x20' (although i may get the larger space, about 15'x40', which has lower ceilings and a much less level floor) :
-Keep all grinding equip. away from precision surfaces. I'm going to have it on wheels near an exterior door, so that I can simnply roll it outside when I use grinding equip.
-Mills go in corners, which i consider to be the most efficient use of space. Either that or flat against a wall, with shelves or tables or both surroundthing the column.
-Keep machines close together, but always have at least one 3x3 table-like surface (minimum) within no more than 1 step of the operating position of the machine. Good motivation for keeping machine sclose together is that there's fewer problems with managin chips on the ground.
-Keep tooling near machines. No need to cross the shop for an endmill if I can put shelves near the mill in the first place.
-For the 4'x4' surface plate I'm getting, I'm going to permantly mount it next to a sturdy workbench, but it'll have a 1" thick plywood box around it, such that when it's not in use it extends as more table space.
-Keep the welder in a ventialtion route, such that good air circulation can be achieved with as little as 1 fan.
-Have at least a 6x8' open space nearbye (not a problem for me, the car space is nearly always empty in my basement), so that large projects can be worked on in open space.
-Have at least 3' between all tables and machines, so that I don't have to squeeze between spots, a pet peeve of mine.
have at least one good, well lite and clean surface to sit at when drawing and analyzing plans. Keep it close to welder and machines, but far away from each to avoid chips.
If possible have 1 large space open for another machine, likely a mill, lathe, or small shaper. Chances are it'll be taken up by the cincinatti mill.
These shop specs are easy for me to fufill, since I have noone to answer to for production. Also, I have to deal with relatively few machines. My workhorses will be the 9x42" b-port, 10L SB, 14" floor bandsaw, and welder. The large space for another machine will possibly be filled by a sandblasting cabinet, cincinatti mill, or 16" Reed-Prentice lathe.