Stealth Attic Grow Questions (first timer)

Hi, this is my first post on the forum and its probably questions that have been answered elsewhere. However, I did search and read random threads for a few hours and still had these questions left.

Basically I'm planning a small "stealth" grow in my attic for my first grow attempt. I want to build a smallish box, enough for probably 4 plants. I'm planning on going the CFL route because I simply don't have the cash to dump on real lights. I'm going soil for the same reason. I have a window-mount fan that I plan to use for my intake ventilation. I'll be using bagseed, some seeds from good but mostly from shwag. I'm not really looking for crazy quality, just to grow a nice yield in time for the peak of summer. I'm looking at making a home-made carbon filter.

My questions
1. How big should I make the box? I plan to just switch out my bulbs for the flowering stage instead of having a veg and separate flowering compartment. I'll be moving away in September and don't want to get stuck in the middle of a grow.
2. What is proper lumens per sq ft? I've read 1000 but I'm really just looking for direct confirmation.
3. I plan on using 40-watt equivalent CFLs. The packaging says they only use 14 watts, but I'm not sure which figure to use when I'm trying to predict my harvest. For example, I read in one thread that I can expect about 0.3gs per watt, so I want to use the larger figure of 40, but I'm not 100% sure.
4. How much of an issue will odor be with a homemade filter? As it will be in my attic I don't want it to stink the whole house out.
5. Using the window-mount fan for intake, do I need an exhaust fan? I feel like it should push the air out through the filter, especially for a small box, but again I'm not 100% sure and dont want to fuck up.

That's all I can think of for now. Hopefully you guys can help me out, because currently I feel overwhelmed. And sorry if you've seen these questions a million times. Thanks!

First timer growers like your self are prone to making silly mistake that can wreck a whole crop in the matter of days,it usually due to over watering or over feeding,an the amount of yeild you get depends on a few things like your enviroment ,ph-ec/ppm/cf lack of light,your temps need to rite as well day an night for your ventilation add your grow room/tent width height an depth together an times it by 60 then u will no how much air has got to b pulled out say you hada tent that was 1.2 x 1.2 x 2.0 you would need a extractor fan that would move 264 cubic feet so that means you would need a good 4" rvk or you might get away with one of those cheap tt100 they have on e-bay at the moment,you need to be pulling more air out than you put inn or there will be negative pressure an the filter will not get rid of the smells,as for the light if you go on e-bay an have look there are 600watt hps with a dual spectrum bulb on hydrovate for £56.00 now thats cheap they may not be the best of the best but they will with out a dout do a good job,im sure you will find a good enough hps light if you look about,the usa must have some cheap light an filter kits for you....good luck any way mate,i no i not answered your ? to how you would like me to im sure some one will soon try going on uk420.co.uk an see what they all say over there on that site