How many parts to keep on hand is whatever makes you comfortable. You do need enough so you don't run out, afterall what would you do if your last atty failed and it's a 3 day wait for replacements? Most of us would go buy smokes. But everyone has a different comfort level. The minimum I'd keep on hand is at least one spare batt, 2 atty's, a box of carto's, a bag of filler material (if I used cart's, which I don't anymore), an extra drip tip, an extra charger, and enough juice to last for a month. But, that's a minimum for me. With what I've got on hand I could easily vape away for oh, 1 1/2 years. Yeah, I'm comfortable with that.
In my experience, cartridges can be used for about a day when new. Then the filler material starts to get compacted a bit and it doesn't make contact with the bridge in the atomizer. You can fluff it up a bit with a pin or needle and it will work for a while. Eventually you just replace it with new filler. You can keep using the same cartridges until they start fitting loose. To fill a cartridge, just remove it from the atomizer and turn it over. Drip juice into the filler material until it looks damp. If juice puddles in it, it's over filled. When that happens, either suck a bit back out with the bottle, or dob it out with a tissue. An easier route, in my opinion, is to use a drip tip. You never have to mess with it. Drip 3 drops, puff away, no fuss, no muss. You get around 12 good hits, then drip again.
If you're wanting more throat hit, try LR atty's. Also try different brands of juice. If you only like vanilla, there's lots of different juice vendors to try. Personally, I like vanilla but not by itself too much. I mix it with a mild tobacco flavor at a 1:3 ratio and it's a lot tastier in my opinion. If you're wanting more TH, some people add everclear to their juice to acheive that effect. Personally, I'd just try the kit as it comes. You can always tinker with things later if it doesn't meet your expectations.
