Welcome to the thread Timastyle.
To see if your internal board is shifting, you can try this:
Remove your e-juice tank and your battery and hold the fire button on the side without pressing it so it can't rattle. Now shake the device and see if you hear any movement inside. Can you see that the black button underneath is in a new position depending on how you shake the device? If you can confirm that it is moving, then it's very likely that the circuit card has broken loose and can now shift from the battery tension below. If you can confirm this, you'll have to decide on whether to return it or attempt to fix it yourself. I might consider returning it since you mention that you "may" have other problems with your device. Hopefully you'll get it figured out soon.
I don't have a V5, so I'm sorry that I can't offer you better advice. I haven't read about anyone complaining about the top cap getting too hot to touch. That sounds like something you definitely want to avoid. I don't vape anywhere near 12 watts on my V3. Maybe a bad electrical connection at the 510 connector providing too much resistance/heat? Clean that up real well and try again. Aside from that all I can think of is to make sure you don't have it in Battery Charger mode. I believe it's the last menu option (menu 9?). You're probably aware of it, but just thought I'd throw it out there. A reduction in the wattage as you vape also seems very strange, but again, I don't have a V5 and there might be something in the menu I'm not aware of. Is there an RMS and MEAN setting? Make sure it's in RMS.
If it's getting hot in your pocket, chances are the fire button is getting pushed. You might want to turn the device off before you put it in your pocket to keep that from happening. If it still happens, then you know something is definitely wrong.
As far as the 30-guage Kanthal, try to reduce that to 5 or 6 wraps and see where your ohms are at. It's hard to say because it will also vary depending on how wide your coil is. Kanthal A1 30-gauge wire is roughly 0.72 ohms per inch. You probably just have to experiment with your Kanthal gauge and # of wraps to get the resistance you're looking for and discover what's best for you. There are a lot of tutorials out there, as I'm sure you already know.
If you want to be sure about whether you have 30 gauge Kanthal, you'll probably have to measure the thickness with a micrometer (if you have one or know someone who does). 30 gauge Kanthal average wire diameter is 0.01 in. (0.254 mm). You can buy a decent micrometer pretty cheap at
Harbor Freight from $10 to $20. I don't know if it's worth buying one just to check your wire. Best thing might be to just borrow one from someone you know.