Before I deconstruct your post realsis: No offense intended.
In my opinion, i would get protected.
Don't get protected batteries, as they aren't meant for vaping. What you're looking for are IMR Safe Chemistry batteries.
I would also get at least 30 amp..
I'm not sure 30A 18650 batteries exist at all. VTC5's haven't been made by Sony for about a year now, and the 35A Efests are actually re-wrapped LG HE2's (20A continuous). That said, 20A batteries should be plenty fine unless you're building lower than .22 ohms. You shouldn't really need to build lower than .3 anyway.. Which brings me to this:
the thing is when your using a mechanical mod you absolutely MUST know Ohms law and be able to work the formulas because it is absolutely necessary to know ohms, volts, amps, and wattage for you safety. If you Don't care for math Android has a great free application that all you do in plug in your ohms and wattage numbers and it perfectly calculates your Amps and volts. The app is simply called ohms law. Problems Wil arrive if you push your battery past it's amp limit. So if your going to use a mechanical make certain you have a excellent rated battery with a high amp limit.
This is very, very true. You can also use
Steam Engine for coil calculations (they have other neat calculators too).
Also make sure you have a ohm reader. You can get a digital one with a 510 connector fairly cheap off ebay or Amazon. Com.
I'd recommend looking places other than eBay or Amazon, just because there is potential for unreliability from third-party retailers.
RTD Vapor is a great site for batteries.
Illumn is also good, but you need to really know what you're looking for because they sell many batteries that would not be good for vaping.
So to make things simple, these would be appropriate batteries for vaping with a mech mod:
SAMSUNG INR18650-25R 2500MAH
EFEST IMR 18650 2500MAH 35AMP FLAT TOP (Keep in mind, this battery has a 20A limit despite saying it has a 35A limit) -- they are still good batteries nonetheless.
LG 18650HE4 2500MAH (I've been using these batteries the last few weeks, they work great. People have been calling them "VTC-killers".)