S10 blowthrough help

I'm going a start a blowthrough project on my singlecab s10. Im going to be using 2 hdc3 subs and can't decide between 12s or 15s. I'm going for spl obv given the subs I'm using. Someone help me out here on deciding sub size. Also I'm torn between a 4th order (confused as hll on how to build one that will sound good) or a regular slot ported box... I'm leaning towards ported. Should I make 2 chambers w 2 ports. Or a single chamber w one port? Helllp.lol