That's a thought, although for sure there are pros and cons going full-active like:
Passive: Impedance rise, once heated, the resistors, conductors, etc. heats up, thus changing the values of the crossover points you have, also it makes the Amplifier work harder amplifying all the signal then the passives would waste them by ditching those that aren't needed, thus the term filter.
Active: No Impedance rise from any external device, your amp would be less stressed because it amplifies only the signal that would actually go in your speakers, thus making your sound more consistent and a clear.
as for your questions, if you plan to go full active, no need to connect the passives, remember the diff between active and passive is where you filter your signal, active: before amplifying, Passive: after amplification, the best way to go active is through your head unit, also , do not be bothered much by the diff bet 2V and 4V, you can gain-match your amp with your HU and also these 2V, 4V values are MAX, not Vrms, by the time you really see 4V out of your HU, you might already hear distortion, if your HU is not full active capable, yes you can go with a an active X-over, like Lanzer vibe X5 or X6, as much as possible, try to get one that has 6 rca's as well, just make sure that you turn ALL x-over and filter to OFF from your HU and do all processing sa x-over, nice thing about external x-over is some also boost your pre-out voltage from 4V up to 8V. also try to amplify every speakers.
