Hi
Having worked for Sage for 9 years I certainly wouldn't say their entry level systems are complicated!
All the things you outlined are the basic mechanics of any accounts system and easily recorded. With regards to stock, again this can be recorded but it will very much depend on what you want to record and how (are you're retailing stock items or just recording stock items for treatment use?).
From an outsiders perspective it sounds like you've not had much experience in using accounts software so my recommendation would be to seek training - you'll only get good information out of a system if you put good information in! It'll be invaluable when you want to start getting more detailed information out in the future that you've created a good set of nominals and recorded info correctly.
Training wise there's loads of options out there from online training to 1-2-1 training. Personally I'd recommend speaking with your accountant as they can ensure you get your nominal ledger setup to your requirements and provide you with a half day training session.
Hope this helps.
Rich
Ps. You cannot 'personalise' the system per se (you can customise reports, you have some definable field labels you customise) but you can always bolt on 3rd party applications that personalise it to your requirements (eg. ePOS system, etc)