I don't play many Tournaments on-line, unless they are Freerolls, Mainly because the returns vary, from Miniscule to a little extra Pocket money, Saying that though they are a great way to get started, I Don't feel comfortable Leaving the House without a £100 in my Pocket and that is just for Taxis, a few Pints and maybe a carry out at the end of the night. So winning a $100 Freeroll Tournament might give me between $30 ad $40 Dollars which is great for a freeroll, but when converted to Pounds(£) not that much, certainly not a night out.
I usually stick to 9 player Sit and Go Games which are quicker than Tournaments and can be a lot of Fun, but as a Strong rule I don't buy-in for anything more than 1% of my total bankroll, for 2 reasons I only play on-line for Fun and I want to conserve the small Bankroll I have built for free.$600 Dollars may seem pitiful to some players Who might deposit $1,000 Dollars a month and play Higher stakes, But I don't play On-line to make Money, I certainly cannot see my opponents when I play on-line, and I don't always trust the Internet connection to stay strong enough to finish the games I play. For that kind of money I will stick with Live games in a Casino.
But moving up in Stakes is difficult when you have done well at one level, and decide to try bigger stakes, It can take you out of your comfort zone and you start to doubt yourself. I used to play Stud Poker on FB. for play money and buying in for 200 Points was great, but when I suddenly jumped to 8,000 Points buy-in I started to lose heavily. After I diagnosed my problem I managed to turn it around and started winning.
You need to understand that the Game hadn't altered, and I certainly was the same player, So what was different? The Stakes, Because I was conscious of a larger buy-in, my playing style had changed, and I wasn't being as aggressive as I was at lower stakes, That is what you need to be aware of when moving up, Don't alter your playing style in higher staked games just because you could lose more than you are prepared to lose. By all means stick to a rigid Bankroll Formulae, but don't be afraid of being yourself, If you are doing well at smaller buy-ins there is nothing stopping you to drop back down to lower stakes if you lose heavily at higher buy-ins.
When the time is right, and you have built your bankroll up to a point where you feel it warrants a higher buy-in, then I would go for it, Just remember be yourself and don't doubt your abilities. Good Luck.