When I started, I promised myself to no let my nails grow because of my job... so many people told me aboute the benefits of playing with long nails that I let them grow until I thought it was the limit for me.
It took, probably, around 2 weeks from very short, then they just get filing and shaping when needed. They just support the fingertips and very little off the tips, like it's always time to trim if I were to, but not enough to be questioned by my clients and/or colleagues. The tone I can get out of the guitar makes me happy, and nails are not much of a headache.
Thumb nail only supports the tip, since it should be considerably longer to use it in playing, and I can't afford to do it.
Regarding nails wearing down, you shouldn't worry about it, since your nail growth compensates for the wear. Just keep and eye on dents and nicks on your nails so your sound is better and you don't scratch yourself or others. A fine grit file is one of your best friends to keep your nails always in shape.
Also you want to start being careful on some daily tasks, or even changing hands to permform them. Zipering your pants with long nails can be a hassle or damage them.