Hold your horses man, I think you're getting way to far ahead of yourself.
To address your first point, vaping at 100+ watts is when people vape sub-ohm, commonly on a dripping atomizer. To vape sub-ohm means to build a coil under 1ohm resistance. I don't know how the "1" was lost in "sub-1-ohm", but I guess the term stuck.
On to your second point. The batteries I believe you are talking about, the ones with relevant amp limits and what not, are standardized removeable cells, commonly seen in the sizes 18650 and 18350, although there are other sizes in between. The ego batteries should have their amp rating and such listed by the manufacturer, although It is likely that the intended use is not above 10A or so, as they were intended to be used with pre-made clearomizers at roughly 2ohms. A little twiddling with Ohm's Law should determine how many amps that would be exactly.
About liquids, the more VG you have in it does not dictate a better vape. For a smaller clearomizer such as a protank, ego, or even some nautilus builds, PG is used to thin out the juice so that the wicking material can actually feed the e-liquid to the actual coil fast enough. Thick juices laden with VG wick much slower, which is why they burn out clearomizers and higher-resistance devices like dropping flies. They also need a much higher heat to vaporize, adding to the problem. However, with builds around 1.5 ohms and lower, more and more vg can be used to thicken up the juice and help increase vapor production without unnecessary stress or harm to your device.
Speaking of coil builds, and particularly having had much experience rebuilding protanks, 1.) they are a royal pita, and 2.) there is essentially only one way to build a coil that'll fit into the coil head shroud. There isn't much variation to be had there. If you really want to rebuild it, the best way is to see how the original came out and do it exactly like that. If you try and get too fancy, It is likely that your coil will either a. not fit, b. short against the sides of the shroud, or c. set off the protection circuit in your battery, and then you'll have to start all over again. Rebuilding a protank is no small feat, and I'm glad you're up for the challenge.
If you're really into rebuilding, I would recommend getting a dripping atomizer and appropriate mechanical or vv/vw (variable voltage/variable wattage) device. A dripping atomizer would give you the space to work on trying new coil builds and various wicking techniques, and a small ego battery would be unable to power such a device, making a more powerful power supply necessary.
Most people who don't like the rebuildable dripping atomizers (RDA) often complain that they want a device that will work on command, requires no fiddling, and produces just enough vapor to get their nicotine hit and that's enough for them. For people like me, and at least as far as you've said, you as well, it's more of a hobbyist thing, rebuilding and such, twiddling, tweaking, making adjustments, trying new things, and experimenting to get the biggest clouds and/or best flavour.
Best of luck to you, let me know if you have more questions. The world of vaping is very, very big.