VariRec has nothing to do with AutoStrategy. You can use VariRec to calibrate the laser power, which is more toward advanced users.
Plextor has design an optimized strategy for each known media and stored in the "firmware". For each media code you use that is not in the firmware, PX716 will create a new entry in the AutoStrategy database, which is located differently than the firmware. We can delete the entries in the AS database but we cannot delete the entries in the firmware.
I've tried Mitsubishi and Taiyo Yuden 48x CDRs without any problem, and I don't use VariRec. Both media codes (Mitsubishi and TY) are supported in the firmware, so you won't see any entries in the AS database. Remember, the AutoStrategy will create an entry if you use an "unknown" or "unsupported" media.
Answer to #3: If you use VariRec, which means you know how to calibrate the laser power for your Verbatim DLP Azo, the recording speed is limited to 4x and 8x only. I would only suggest using VariRec if you know what you're doing. Otherwise, try without VariRec and use the certified speed of the Verbatim, or you can use a lower speed: 32x, 16x, 8x and 4x.