I very rarely have trouble with dry hits with the M3M, idk. I think the .5s are actually better in that regard than the .3s.
1. 70% VG max IMO, maybe even thinner if you can take it.
2. As with all factory coils, start low and work your way up. With a fresh coil I start at 10W, take a couple of puffs, increase to 15W, take a couple of puffs, etc. until I get to where I want to be.
3. I personally tend to keep the airflow wide open all the time.
4. Lower your power. The .3 CANNOT take what they recommend, power-wise. I usually vape the .3s around 40W, +/- 5W. Obviously this is partially personal preference, but I would put money on the guess that vaping it at 4+V has something to do with your dry hits. Although I'm not totally sure why you're having this problem with the .5, which I usually do vape at 40-50W and I have had very few problems with.
5. Try out the ECL coils, which have larger wicking holes.
6. Take primer puffs, puffing every so often without firing, ideally with the airflow closed.
7. Avoid extensive chain vaping.
None of this is earth shattering stuff, but as I said above, I have had almost no complaints with dry hits with this tank. Every so often I'll get a bum coil, otherwise they work until they don't. My guess would be that going with a thinner liquid (depending, not sure what you're using) will help a lot.
Once your cotton is burnt, it's not going to taste good. So if your hits were bone dry, yeah, this current coil could be done for. If it was more of a "warning" dry hit, it may still taste OK when well-saturated. Either way, it will start to go downhill quickly once singed.
I'd personally recommend the Pico 25 over the AL85 for a variety of reasons, if you're going to do something like that.