Aside from pre-outs, also look for features. It's not fair for me to simply judge a head unit based on price and brand, but if you want a blind vote, I'll pick the Pioneer since it's more affordable.

Yes, you can just bridge it for the subwoofer and use the remaining two channels for your frontstage which will have passive crossovers naman.

The only reason you might want to get a monoblock is if you think you need more power whether that be more watts at a given ohms or you plan on lessening the resistance (ohms) to get more power. Monoblocks excel because a lot of them are stable given 2-ohms and the more expensive ones are stable up to 1 ohm. On the otherhand, 4 channel bridging is usually stuck at 4 ohms.