you can improve rhythm by taking up playing the drums. this is fairly drastic but it works !!!

IMHO one of the secrets of great vibrato is to have strong fingers. The best way to do this is just to practice. One of the hardest vibratoesq moves it to bend a two half steps up to a note and then add vibrato. I couldn't do this when I first tried but it comes with practice. You will probably find that it is easier to do by pulling your fingers towards your palm than the other way round though eventually, you wan tot aim to do it both ways round.

Oh and the secret is practice !!