Making the decision to switch from the pre-filled cartridges to blanks is a logical next step in your vaping experience. Those cartridges are way over-priced and do not last as long as advertised, as you have found out. Do be aware that you need not limit yourself to V2's eliquids. There's literally a whole universe of flavors and vendors available to you.
Check out the two juice forums here for ideas of what e-juice vendors people are using and then look those websites up.
Many online e-juice vendors offer inexpensive sampler packs of there line of flavors, with the intent for you to buy more of the flavors that you like. Beginning with this practice is good for you so that you do not waste money on larger bottles of juice that you may not care for. I'd also encourage you to try different flavors and not limit yourself to tobacco or menthol flavors. You'll be surprised what you will like, and is one of the things that vaping has over the analogs.
And yes, vaping more than you smoked is normal. And healthier. Your body will let you know if you are getting too much nicotine in your system. The same symptoms as another stimulant, caffeine. Jitteryness, nervousness, headache.
Vape as much and as frequent as you like. When you feel the desire for a cigarette, vape even more frequently for a period of time to get more nicotine into your system.