1 Clean clamps don't slip much. Dirty clamps slip a lot. So make sure your clamps are always clean first and foremost. I like to take a clamp and clamp a loop of string then pull 60 lbs of tension on the string and adjust the clamp to where it just does not slip. Then get the feel of how much pressure it takes to close the clamp.
2 It is possible any instructions could be wrong. Figure out what you are doing and depend on how to string not instructions someone else uses to at track you to their website or service. Where ever the mains end then are usually two tie off grommet holes on each side of the racket. Identify both usually one is on a main and the other on a cross then there is not problem figuring out which one is for which. When they are both on a main tie the mains off at the one closest to the last main you tensioned.
T = Top or Throat B = Bottom H = Head
3 Yes it is caused drawback
4 I like to use a starting clamp to tie knot and have started using a VS Starting knot for all my knots. If you do not have a starting clamp you could wrap the string around anything (like a dowel.) when tying knots do not under any circumstances use a double half hitch, most people don't even know how to tie it. YULitle's video on how to tie a DHH is a perfect example of how not to tie a DHH. When you cinch up what ever knot you use pull firmly but not too hard. Then complete the second portion of you knot with a little less pressure. Before you remove your clamp hold pressure on the tail of the knot and keep that pressure on until the clamp is off then trim your tail.
Good luck and with practice it will come much easier.
I would like to apologize to anyone I have not offended. Please be patient I will get to you shortly.