look at it this way,delay painting and save up for the extra ltrs you will be kick your own ass when you accidently buff through the layers into primer.
And trust me i wouldn't be painting 2k with just a charcoal mask,it's your lungs,!1yr ago a fella was found dead in has garage spraying 2k as some products use cynide as a catylast to set the paint off.
Im a steam fitter and turner by trade i work for a tourist railway and have just painted a steam loco and that required 38 ltrs of paint and clear,Im just about to paint another

.
I sprayed an xy mocky for a friend and that use's 12ltr of wild violet and clear,it not worth using too little product.
Acrylic is the best way to go for home use,and yes you can getaway with a charcoal canister mask.
if you want a 2k look then there are many clear coats (iso clears) that require a hardner that will give you the same finish,but the clear will alter the colour slightly..
you will only require a clear if the colour is a metalic,which means you will have to spray it with no peal and give at least 3-4 coats of clear light rub with 1200 before the last wet coat.
hope this help's
ps be safe as these are harmful product ,even if it is just one time!
cheers Anthony