The filler should look glassy, but not have a pool of juice on top. If you fill it with a little too much, just dab the top quick with a paper towel and it'll suck up the extra.
Vape as much as you want, if you still feel like you need a cigarette try increasing the nicotine level. What I recommend is ordering a bottle of the strongest stuff your supplier sells (normally 36mg, some go higher) and a bottle of the lowest (0mg is best) of the same flavor. That way you can use a third (empty) bottle and use the 0mg to cut it down (ie 50% 36mg and 50% 0mg = 18mg). Once you find the right level for you (enough that you don't crave cigarettes, but low enough that you don't feel dizzy or sick from too much nicotine) then you just order that level (or the closest you can find).
Only thing you really want to watch out for with overuse is not letting it cool down. Puffing away every second for 10 minutes is a good way to burn our the atomizer quickly. My general rule is 3-4 good puffs then 30 seconds to cool down. If you want to chain vape for long periods, just carry 2 PVs and switch every 3-4 puffs. If the atomizer feels warm, let it cool down. You're not going to hurt yourself, but once the atomizer is burned it will taste like burnt plastic and you'll need to buy a new one. Always have at least 1 spare atomizer around in case you burn one out (I have like 50, but i'm a hoarder).
Juice in your mouth won't hurt you, might lead to heartburn if you get a bit too much (but that would mean you over filled it repeatedly and swallowed a few drops), nor will getting it on your skin. You'd have to be dealing with 100mg levels (which some people who mix their own use, and then cut it down to lower levels) before you really need to worry (I've spilled some of that on me, cleaned off quickly but still felt like crap for a little bit).
