Honestly, if you are good at it, it doesn't matter how much you start with. I bet with another person who has a huge bankroll and bets on 1-3 games a day maximum, he makes around +30% bankroll a month usually. http://imgur.com/6fnfkiQ That's his stats for the last week or so.
Me on the other hand play a bit more wild and made £20 - £1080 in the same time period (http://imgur.com/eIUWqY1 - http://imgur.com/NbFkB95). I will probably continue to have high odds horse bets and corner bets and stuff on like I always have but will chill out on the % of my bankroll I have on each bet and amounts in general bet. For example today I had £50 on ODD BK 0.0 (refund) and £50 on Norrokoping 0.0 (won) and a few in-play/horse bets of £1-25 - over all day profit of about £95.
So... to kinda round up what I am saying.
Each to his own. My mate thinks I am a bit mental having £20 on a horse @7/1, and I think he is a bit mental having £700 on a football team... but as long as we both keep making money..
A points system with a low starting amount will work... eventually.. but it's going to be slow and boring. There's nothing wrong with going a bit hell for leather at the start, lumping 50% of your bankroll on something.. but once you do have a bankroll of an amount you feel attached to.. it's best to chill it out, maybe start to think of a points system then.. but it is totally worth using say £20 of the £500 you were going to put in and see if you can make it £500 anyways...
If you want I can hook you up with my mate, he runs a premium betting group and his stats pretty much always look like that. I have bet with him for years now so can vouch for him. Though he isn't perfect and I know today his bet lost (it was on Ruch Chorzow), I think he charges like £10 a month or summut. I don't subscribe to it personally as it isn't really my kind of thing and I feel like I am about on skill level with him betting wise anyway.. but yeah.. it's an option anyways. I know he does a free trial type thing and you can see for yourself if it's for you or not. If you are 100% going to lump £500 into an account, I would recommend at least considering expert tips.