1. I think this is a fine idea if you're willing to accept the risk that it'll ruin your bike.
2. I hacksawed off a brake bridge and cable guides on an old fixie conversion and got all kinds of grief from BF folks, but it was fine.
3. It probably won't work. And I would definitely not drill handlebars... but that's me... broke a set once because it fatigued under the wrap and I couldn't see it.
4. I love my internal cables - I also love that other people can't figure out how to work on them... I also like gluing sew-ups, and I hate the fussiness of disk brakes. So chacon au son gous or something like that.

Photo for cred:
Note how the tube shape is changed around the penetrations - these are not just drilled into the frame, they are planned and fabricated. Also the penetrations are cable stops so there's no housing inside the tubes. The housing liner shown in this photo is how you get the cables in there, and use it to hold your place when you're taking cables out.