The eleaf invoke is about the smallest, lightest 2 battery mod that I recommend highly. It's just well built, and tiny in form factor and weight compared to most 2 battery mods. It's high quality build, despite being lightweight. Since it's unclear yet whether you will be a MTL vaper or DL vaper (the crown does have some higher ohm coils, but it's really a crossover tank in my opinion, which isn't bad, but you may find yourself preferring more wattage and lower resistance than previously, so it wouldn't make for a bad "starter" tank and you can try out the various coils. The battery life on the eleaf invoke is pretty decent, it does a good job taking power from the batteries efficiently.
If you want to go with a single battery mod, my guess is that you WILL require bringing at least two batteries with you to be on the safe side. The pico is very inefficient at power conversion in my opinion, although I only got their "first" removable battery kit. I honestly didn't care for it much, although if you get the mod, I would definitely recommend the mod only. The only issue would be if your toolbox ever gets insanely warm in summers, but if that is the case, I don't recommend storing batteries in that environment for long. If it's not a problem where you live, you could really go either way. I prefer carrying around a two battery mod if I am leaving the house for long periods, it's just easier. Or I grab a couple single battery mods.
Good MTL tanks around at the moment: The nautilus 2, the Kabuki (can start with a clone from Fasttech if willing to wait, to see how you like it) the original is expensive. I am a fan of the Ijoy elf, which pretty much vapes like the nautilus 2 (and accepts those coils) only it fixes many "problems" with the N2, like better capacity, easier topfill, and I think, better flavor. The other tank I might recommend would be the Ego One Mega V2, but not paired with the coils it comes with, but the Joytech CLR coils at 1.0 resistance (they also make a 0.5 resistance coil, I believe, if you wind up wanting something more airy. Good fill capacity, the CLR coils have awesome longevity and flavor. They can also be rewicked and recoiled very easily, so it can be a cost effective vape.
Best of luck. As to nicotine, if you go more MTL I'd recommend starting fairly high, although it is likely with any setup you will be getting a bit more vaper than some of the older setups. The idea of buying small "tester' bottles including one with 0 nic is a good one, as if your nic is too high, you can just dilute as needed. I was a 3 ppd smoker and vape at 18 mg nicotine, but somewhere in the range of 12--36 mg/ml is typical for most people starting to vape.... If you go more sub0hm with low, low resistance, at that point I would recommend a nicotine level between 3--9 m.g., depending on how often you vape, and what winds up being a "satisfying" nicotine level for you.
Best of luck, I did not quit on my first vaping attempt either, but this time around it was totally different. Wishing you all the luck in the world!
Anna