Personally I wouldn't add more than one account per GB so if you have 15GB 15 accounts max. You could allocate 200-500 MB per client but your still going to fall far short of 300 accounts.
Its not worth it to make your clients suffer from either slow servers because they're overloaded or sites that suffer downtime.
And yes a VPS can handle multiple accounts. If your aiming for several hundred you may as well go with a managed dedicated server if its within your budget, but starting out with a good VPS to test the market would be wise. you may find it tougher than you think to sell that many accounts.
Last edited by musicman153; 04-24-2011 at 08:57 PM.
If your just starting out then being a reseller is a good option. Just try to plan for the future so when it is time to upgrade you can. What type of hosting are you wanting to do? Windows hosting or Linux? It could matter depending on where you get your reseller account at. Most hosts the offer reseller plans will probably be able to help you and answer your questions regarding, where to start, upgrade options, vps, standard server, dedicated servers and so on.
If you're still a newbie on this business, I recommend you to start with reseller account first then upgrade it when you think you already need a VPS. Still, it's better to have a nice experience on different accounts.