Welcome to VT, there is a lot to learn in the beginning, but in no time you will get the hang of refilling. Ask any questions you have, there are lots of friendly people here
This is by far the scariest question I've ever encountered. Why on earth, would you want to place high strength liquid nicotine directly on to your skin. That's like asking how much caffeine you can safely inject into your bloodstream for a "buzz." I'm also not sure why having a mortgage and car payment entitles you to anything other than having a home and a car.
You are exactly the reason why bottled liquid will no longer be available when FDA regulation kicks in. Please, for god sakes, don't pour liquid directly on to your skin. It's a one way ticket to nicotine poisoning.