well I guess when you decide to take it to the next level as a hobby you'll get a domain and hosting ... though having built up your following on the blogger ? site it'd be a bit weird ...
Start as you mean to continue I would suggest ...
40 quid though is 40 quid ... and its a re occuring expense every year ... but its a lot more fun in my opinion to have something you can really mess with ... alter the theme ... have your own me@mydomain email address and so on