1) Better attach the string to the bow, I can't see to find any good way of doing it.
Have you looked online how to actually string bows? Because that is exactly how you do, you're just missing the notch:
That is just one type of notch, there are loads of ways to do it.
2) Have something "Holding" the metal plate with the spikes to the wood base. Something like string or leather. I tried a few methods and couldn't do it.
Realistically speaking there
shouldn't be anything more holding the spike plate the the bow because the metal would not bend. Bows do:
Yes the spike plate is highly unrealistic but it's fine. Just keep it as is, attached at the handle
Just add the notch and you're done.