More air = less harsh, it wouldn't cause a harser hit.
Tighter draw = harser hit.
And for the other questions i think they're already answered.
Welcome to the forums TS.
About modding the PT3 (mini)... It already crossed my mind. I would need to build two 4 Ohm coils to make a 2 Ohm atty. There is only one little problem... I've never did that before and although I feel that I'm able to do something like that, I have no experience and what can be found on the net is rather vague... I happen to have some kenthal A1 wire but its 29 gauge (0.30mm) and I think thats WAY to thick to build a high Ohm setup in a limited space like the PT3. Maybe I'll get my hands on 32 gauge wire and try something like 10 turns to make a higher Ohm setup.
You might want to just rebuild build your atomizers with a single coil. That's what I do on my MPT3. I'm sure you can easily fit a 2 ohm coil in there with 29 ga. I use 30 ga and have plenty of room.