You seem to have quite a few concerns, John. 67 views and no takers generally means that everyone (capable of answering) thinks you're one of the seemingly endless number of highly dangerous people who want to do deep sub-ohm without actually learning anything before hand, and... no one wants to invest the time.
Without going into the details of why, I sense you are sincere in your desire to learn... so I'll take the time.
Lets see if we can attend to a few of your issues, and get you pointed in the right direction. Apologies if I make assumptions about what you do and don't know... that's the nature of the interweb.
I'm more concerned with what you know and what you have available to you. Do you have an accurate ohm meter... be it a build box or a DMM? At 0.15Ω, if your meter is off by 0.05Ω, your draw can jump from 28 amps to 42 at 4.2V.
If you don't have one, buy a good quality build box, and preferably a decent DMM (with good quality test leads) as well. If you want to get really tricky, Tech-Thing makes a neat
milliohm converter module for standard pattern DMMs that turns your two wire DMM in to a poor man's 4 wire milliohm meter.
How are you at Ohm's law calculation... either paper and pencil math, or using one of the may available on-line calculators. I suspect not so much, or you'd not be asking the "is this safe" question... rather doing the calculation and knowing for yourself.
Click on my second sig line hyperlink and have a read... knowledge from people who actually know stuff is better than guessing, or getting incomplete responses from "some dude on the interweb". ;-)
There are so many discussions on batteries these days... what's real and what's BS... I don't blame you for being concerned there. Personally, I use only genuine MNKE, Efest, Sony, Panasonic and AW batteries that I buy from one source...
RTD Vapor. I trust Randy to sell only authentic products.
That last bit is about the best you can do these days... buy from a reputable seller like RTD. RTD does sell the XTAR 30A, and they identify them as Sony VTC4 based cells. Re-wrapping is quite the common practice... hell, genuine AWs are "selected" name brand re-wraps.
On your mechs. They are sort of "old style" in the sense that they probably (hard to say with clones sometimes, what you end up with) don't have telescoping 510 pins... just floaters or single screws.
Sometimes what you have to do is create a "dedicated" mech and atty. If you have a gap, shorten the mech 510 top cap pin so that everything ends up flush with selected, dedicated atomizers & batteries. I don't know if your mechanical... but a grinder, file - even course emery cloth will take a 1/16" off the end of a pin. If you do shorten them, get the end as square and true as you can to insure good conductivity.
Why the mech pin and not the atty? Mech pins (like those in your mechs) are just lengths of common metric screw thread, and easily replaced (my local hardware store actually has a decent selection of metric copper and brass screws). Atty 510 pins are often unique machined parts that you can't find at the local hardware store.
If you Google a bit, there's a chart of common vape batteries on the interweb, that includes their actual measured length. It's a bit dated, but you still might find it useful for comparison purposes.
That's about all I have. If you've not found a handy coil modeling calculator yet... Steam Engine (see first sigline hyperlink) is one of the best. Remember, "garbage in - garbage out". If you need help translating the available options, shoot me a PM, be happy to help.
Be safe.
