Some answers:
Refill your cartridges as they get dry. Assuming you have the standard 510 cartridges (not something larger), that's probably around the equivalent of 3-4 cigarettes worth of use. If you start getting a burnt taste, it's definitely time to refill.
juice taste is pretty personal, and what one person likes another will hate. However if you're looking for that analog taste I've been told
PureCig from FSUSA is about the closest you'll get. Note that "tobacco" flavors are going to taste more like the un-burned tobacco smells in a cigarette rather than the ashy flavor from actually smoking. I'd recommend checking out the suppliers forums and getting a bunch of 5ml samples from multiple places. I've had good luck with FSUSA, Backwoods Brew, Gourmet Vapor, and VapeRite but there are plenty of other juice companies that you can try.
A drip tip is exactly how it sounds -- a tip that you plug into your atomizer instead of a cartridge that allows you to drip juice directly onto the atomizer. Many people prefer to drip rather than refilling carts all the time. You'll get 3-5 puffs off of every 2-3 drips or so, which means it's more work to do but you also get better flavor (not muted by the filler) and you don't risk the cartridge running dry. For now, I'd suggest sticking to your carts until you're comfortable with vaping. Read a bunch of info here and in the ECF library, and then see where it takes you.