both the IMC and aerobatics are worth doing as both will increase you skill , i would advise the IMC first as CFIT seems to be the biggest killer of PPL holders.
As for the aerobatics i would start with a low powered aircraft such as a chipmunk as it is takes more skill to fly good basic aerobatics in a chipmunk than an extra.
As for the yak i,v not flown one but i,m sure its great fun but remember as with all high powerd aerobatic aircraft your lookout is imperitive as other pilots are not expecting some of the manovers that will become your stock in trade and so there lookout may not be as sharp as you my wish also it gives you a responsibility to avoid these manovers in areas of high trafic density.
What ever you decide to do have fun and be safe !.