1. Take a straight pin and put a hole or two through juice holes on the side of the housing all the way through vertical coils to the other side. Cotton may be packed too tight.
I do this with the horizontal coils before I use them. The cotton on the verticals seems to be packed even tighter so I tried this, as well as fanning a tad bit of cotton out of the holes.
2. Must your wattage be at that level?
No. I'd vape all the way up to 50 (max on my mod) as long as it provided good flavor that isn't too hot. I vape at the wattage I use because anything higher usually results in a burnt taste. A couple things that I've noticed is that I seem to have better luck at higher watts when using a lower resistance coil and a high quality juice such as Charlie's Chalk Dust or Fuzion Vapors.
3. You can use same housing of vertical coils to recoil and wick horizontal coils.
I'm just starting to get into messing with rebuilding coils, basically so I can keep using the horizontal coils until I figure out a better solution.
4. If you've got any ProTank 2 coils laying around, they can be used especially if you rebuild them too.
I do not. The only other tank I have used is an Aspire Nautilus mini, I think. I despised that tank but also hate throwing things away so I still have it. It's cracked and the airflow is horrendous. I'm actually using it now as I'm currently messing with the coils on the Subtank. It doesn't leak even though it's cracked, but it's like trying to suck a golf ball through a garden hose.
I've been vaping for a long time; started off on an old Lavatube. With that said, I never got into the intricacies of doing it right. I underestimated how in-depth things can get. Making matters even more difficult is the fact that the hardware has changed so much in such a short time...it's hard for me to comprehend how much everything has changed for the better since I started out.
To avoid a tl;dr, I will wrap this up. I've recently found myself more interested in getting the best vaping experience I can. That involves a lot of time, a bit of money, and the help of people that are willing to take the time to answer questions, such as yourself and others here. I'm 100% confident that my issues are user error and not equipment related. Tons of people vape on the same stuff I do and can vape 50w with no burnt flavor. I'll get it right eventually.
Hope this helps.