Well, this is gonna be an easy one, I do most my buying through Cignot.com and ONLY have 510s laying around here.
How much liquid do you put in on? That's hard to say, it really depends upon what type of filler you are using. If you are using what came with the kit, you would fill it up until the top of filler shows a liquid.
How do you do that by dripping. Well, I don't, I use an eye dropper. It is a short but skinny eyedropper. I shove it down the side of the cartridge (as far as I can get it) and start squeezing the
juice out of the eyedropper.
What this does? It filles the cartridge from the bottom up--any trapped air is forced out of the cartridge--you get more
juice into the cartridge that way.
(I use pyramid tea bag material)...it doesn't trap the liquid inside.
Do you need to clean/replace the filler? Not really. If it starts tasting bad or something, pull the filler out and run it under hot water--squash it many times like a spongue, then stuff it back inside the cartridge. (probably, within a week, you'll wind up having to replace the filler any way).
Bigger unit? I don't know, 510 and 901 are the two biggest I have. BUT, if you get a Little Chuck or a Protogy (I think I spelled that last one right)...the
batteries are reported to last all day. A place called Vapor King sells 'mega' batteries for the 510.
Somebody else will tell you about the 'bigger' models.