Welcome man... The CRX is a fun a little car... And its the lightest Honda (too my knowledge), due to its 'small package', the fact its been around for some time now, its got literally TONs of different things you can do to them... From swapping in another D series with VTEC, a D series with DOHC, or the mighty K series from an RSX... If its a Honda engine worth swapping, I can guarantee its been done to the CRX before... So theres plenty of information out there...
Basically my best advice is plan what you want to do with the build, what are you building it for? Show, strip, street, or track? And go from there... Because depending on that is basically determines where to start... My own personal favorite engine for the CRX is the B18C1 (Integra GSR), the reason is, its reasonably priced (for the power it provides), not too heavy for the chasis, has a decent amount of power, tons of aftermarket support, is a newer engine so less wear and tear, plus you can pretty much do whatever kind of competition with it, from drag (its got a decent amount of torque compared to the B16 so its better off the line than a B16), autox, and would be nice to have just driving around town from day to day... Then theres suspension mods, which also depends on what kind of driving you will do with the car...
As for any sites, basically just reading forums is the best way to learn... This one,
www.honda-tech.com,
www.honda-acura.net,
www.ef-honda.com,
www.efsource.net,
www.crxpower.com, and others...