I use the Poly Capo to replace one song where I used to use a capo, it saves time and retuning etc. But for drop-tunings I still use a Digitech Drop, mainly because of the DSP usage.
1) Are you running effects in front of the pitch effect, or after it? Majority of the time, pitch effects should be before any other effects in your chain.
2) No, stick to what you're doing, if I'm understanding you correctly.
3)For single note stuff, Simple Pitch is fine. But as @rd2rk says, if you want chords and everything else, Poly Capo is your best bet.