Sorry but I have to 'beg' to differ to some things here, from experience.
1) It does not take 'years' to get 300 clients, I had that in the first year, probably more.
2) One man can manage 300 clients, trust me.
It is not as hard as you think, providing you work hard and keep up with the game!
Your average out of about 1000 clients, not even 100 would regularly send tickets, if you are not advertising for the 'newbs' of the web.
But 300 new clients a month, might be hard, but still, they all have to be sending tickets to make it hard.
So providing most know what they are doing, and most do, you will have not so many issues.
The main issue is cash flow, if you cannot handle expansion of servers and the network, then you will not get anywhere.
Now this is when it gets hard.
A friend of mine runs a company, and had 3,000 clients in less than two years, he is a bit more skilled than me LOL!
Either way, he advertised to the newbs of the web, and offered a type of hosting which comes with issues.
He struggled, outsourced support which never did work hardly.
Desk full of 200-400 tickets a day, 10-50 phone calls a day and plenty of chats.
Now the difference is, most of his clients did not know much about hosting and just wanted a 'website like youtube' which was what they did.
Pure example of when you get it wrong.
The money was very high but still, not high enough.