I have a KISS 20" A2 but here lately I've really been wanting a 16" with a flat-top, the only problem is I'm broke, I make enough to pay the bills and thats it, so what should I do?
I plan to put a rail, EO Tech, light, rear BUIS, a CTR stock, and a sling on it (I'll get most of these later), and I plan to use it for hunting, plinking, and home defence.

Trade the A2, 20" upper for a 16" A3 or A4 upper.  Then buy a cheap back BUIS.  Then slowly over time upgrade.

If you don't have much discretionary income where are the "rail, EO Tech, light, rear BUIS, a CTR stock, and a sling" coming from? If you can afford them, just pt a couple items off to get a new upper like the DD 16" upper from PK for $495. Otherwise I agree with the first poster, just trade your A2. 20"'ers are a little tough to come by still so it shouldn't be too tough to sell or trade.

The answer is as simple as the three following choices:

1.  Sell what you have to cover what you want
2.  Trade what you have to get what you want
3.  Stop wanting.

If $$ is tight, makes no sense to spend on extras.  Black Rifle Disease is referred to as a disease for a reason.

I think a lot of us have been in your shoes at one time or another.  I vote for selling your upper, A2 stock, and start accumulating the parts for your "want" rifle.  I am a person who recently must have an Aimpoint/Eotech sight to enjoy and use my carbine due to some eye sight loss in my dominant eye.  Figure out what you need then add the wants.  If you go the carbine route and need a red dot sight then make that the priority.  To be honest, the railed hgs make it too easy to add stuff and weight to a carbine.  I am really thinking about ditching my KAC railed hgs and going back to the OEM M ones.  Just my opinion and it isn't worth a lot except I am a person that likes to trade stuff out all the time LOL.

Do what I did when i was young, single and broke. Have as much cash with held from your paycheck for tax puposes. When you get your return theres your new rifle. I put the accesories on as i could afford them.

Maybe not the best idea for some but worked for me. 1 new rifle a year for 3 years until i got married.

If your already married that  may be part of the problem. Just remember a woman is no replacment for a good AR .. : )