The tfv4, other than the Mini, is probably too fat to fit on a Pico, and you would want more power anyway. You could get a tfv8 Baby Beast, 22mm, though the RBA is sold separately. Toptank would be better match for a Pico. Though there are lots of bundles with the Smok Alien mod, including the Big Baby, which includes the RBA. The standard size Baby goes through its' 3 ml of juice pretty fast. I find the Baby Beasts a nicer vape than my Kanger, but the Kanger is more economical on juice and batteries, and is not bad. There are many other options for a Pico, like the Cleito (not the 120), for which you can buy an RBA separately.
I find any single battery mod goes through battery life pretty quick, unless the power is kept down. I have an IPV D3, another small single battery mod, that I use with the Kanger, at around 30-32w with the 0.5 ohm coil. On the rare occasion that I build, I skip the RBA sections and use a Limitless Plus that I'm not crazy about, and use it with bigger mods. But there are many good RTA and RDTA tanks, and the Baby RBA's are probably better than the typical, as I think of the reviews.
Also, a Toptank is relatively stealthy, but a tfv4 is for clouds, and will attract some attention, wanted or otherwise.
