Hello there,
I can only draw on my own experience to help you consider your situation - although I hired first for a holiday, within half an hour I turned to my partner and said 'I'm buying one of these'. Although utterly clueless as to what owning one really meant I do know lots who have bought without hiring and haven't looked back - so it really depends! I did, in fact, go on to hire a second time 'just to be sure to be sure'.
I spent hundreds of hours looking for a boat that wasn't too old, yet affordable and reasonably comfortable and not too large (over 50ft). Once we found 'the one', we didn't get a survey! We spent a year re-building different rooms in evenings and weekends, e.g. converting a crossover bed to a fixed, building in a dinnette and permanent sofa, refitting the kitchen etc - we had the time, and were also living on the boat so wanted to get it right for us. It sounds like you could do this too?
Two years later (in 2005) we sold her for 10K more than we'd paid and accidentally made a decent enough profit on it! Given the current economic situation in the UK, whether that is feasible now - I don't know.
Knowing what I know now (a little bit above clueless), I would heartily recommend having a survey - I can assure you we just got lucky first time round. And, as I know well, getting a new boat doesn't meant you save yourself from serious problems with the builder. If you do go for a slightly older boat, it's likely you will sell it for more or less than what you paid for it - but you've 'saved the cost of a holiday' (or more) in the interim.
Secondly, the size of the boat comes down to what you want on it. For example a walkthrough bathroom takes less space than an enclosed one, ditto a crossover/fixed bed. Having somewhere to eat from v. a small collapsable coffee table/laps. These issues are personal, so personal in fact some members of CWF will fall out over them! Perhaps your best way of determining length is looking at your minimum needs and calculating from there, e.g. do I want to make a bed up everyday = crossover bed/ or sofa bed in the saloon converting to a bed a night. This way you can work out the length you could live with?
As for shopping - go when it's not raining, or if you're in a marina get your local to deliver!
Best wishes.