Varicella will be waived as it’s not given in the UK.
It won’t slow your application if you have it done at the medical, myself and my family all had to have several jabs each which were done on the day. It’s not cheap though so if you can get them done via your GP instead ahead of it, that would save some cash. You can also get a titre test done to check for immunity, but I’d think that would delay things.
Best of luck.