1. the answer to question number 2 should answer this question, too.2. just get an open-end wrench to tighten the screws in the cups.3. i've had my sundias for a long time now, and i never had to replace anything. if so, the shop you bought the diabolos may also have the fitting axle. if not, there are plenty of shops who have. (just replacing the bearing is probably more work and will cost you more than a new axle)4. mister babache is great, and if you play your string right i should last quite some time. because of that, price should not be something worth considering when choosing a string. i'd recommend getting some bits of string from different manufacturers and just try them out. in the end, you are the person who uses that string, so you should be comfortable with it.hope that helps, Jannis!
To answer question #4, I would HIGHLY recommend Taibolo strings. Some diabolo strings are slippery when you first use them, before the grip sets in. Others have a good grip right away but snap pretty easily. With Taibolo strings, you get the best of both worlds. Good luck with that.