The only problem with putting it all in one log book is that if you do eventually decide to go the whole way and get a PPL(H) it is tidier and easier to send a separate H log book off to the CAA without having to unscramble the H hours out of it.
Why stop at one hour - go for it. I did my first rotary hour 25 years ago and then waited 20 years to finish the course. Looking back I really wish I had completed it then.
Good luck!