2- My scalp and skin is extremely oily. I have to wash my hair every 24 hours, or it will look awful. I'm worried that this will cause me trouble with an hair piece. Do you think I can keep my hair piece for at least 5-7 days, even having an oily scalp?

Hard to say.

You will have to try different glues and tapes to see what gives the best hold.

3- Is it possible to try a topper/full cap without shaving my hair, and make sure it will look good, until I take the plunge for the shaving?

Not really. I would order two full caps and when they arrive make sure the specs are good before you proceed. There are a few critical areas that will determine whether they are useable, and if you post pics or a short video I can tell you if they are going to work. As soon as you get two good units, shave it all off and go for broke.

4- As to costs... I currently spend about 125dollars (perhaps more) every month in products for my hair... do you think the hair piece route will be cheaper or costlier? By how much?

If you care for the units properly you will probably spend less money.

5- As to my girlfriend... I never told her I use concealers. She respects my privacy a lot, and she never interrupts me when I'm in my bathroom. I don't honestly know if she knows I use them, but I try to believe she doesn't. Anyway, our relationship is strong, and I know that one day I'll have to tell her, but I would like to wait at least an year before I would do it. Do you think a well applied hair piece can be undetectable even for someone who is near your almost every day of the week? I'm not worried of her running her hands through my hair, because she fortunately never does it, I'm just worried if it will be noticeable.

A well applied, properly maintained hairpiece is very difficult to detect. To my knowledge no one has ever spotted my hairpiece unless they were told. That doesn't mean that it is impossible to detect, but a good unit is all but impossible to spot.

6- How much time do you think I'll have to spend with the maintenance and adjustment of the hairpiece? How long does it take to clean it? How much time will I have to spend daily adjusting the hairline, etc?

I spend about an hour maybe an hour and a half per week. Cleaning only takes about 20-30 minutes. Daily adjustments aren't necessary unless you expose hairline, and even then you might only have to touch up every few days.

7- Are hair systems detectable in bars/night clubs which have that purple light that makes white things glow?

Get an all lace base and you shouldn't have to worry about that.

8- About the cut... I think I don't have the courage to go to a salon and tell someone "hey, I'm wearing a hair piece, would you please cut it for me?". As such, do you think I could manage to get a decent haircut made by myself?

If you were going to do that what I would do is make sure the base is trimmed up to your liking, and send it to Debbie to get cut in. You will probably still have to tweak it a little, but there is no substitute for a professional cut.