Hi Andrew.
I can't speak to the replaceable batteries, as all my mods are self-contained. "510" is a threading which is compatible with a vast majority of the devices out there. There are other types of threads (901, 808, eGo, etc.) which dictate what type of topper can go on your device. There are adapters which convert one thread style to another (just make sure, if you need to get one of these, that you know which end is your device and which end is your topper.)
Not sure exactly where on the forums, but there are a number of threads regarding the different batteries. I think Baditude has a blog talking about batteries and safety. I'd be inclined to get a DMM (digital multi-meter) if you're going to use replaceable batteries. You will want to check the charge on the battery often (especially if your device doesn't have a built-in volt meter.)
If you're building your own coils, you ABSOLUTELY MUST have an ohmmeter of some sort. My VV3s and MVPs have a built-in reader. I don't drip/sub-ohm, so at this time, I'm comfortable with those internal meters to check my coils. If I ever venture farther up the vape chain, I will probably get some sort of dedicated ohmmeter that can read lower than 1.0 safely.
Keep asking away. Many way smarter than I will be happy to chime in and help you out
Enjoy the