sessions - max number of variables before things get bad?

I'm exploring sessions in PHP4 as I build a new site, and I have decided to rely on them more heavily than in the past. Basically, I'd like to set things up so that when someone logs into the site, all of their accounts variables are queried from a database and loaded into session variables (we're talking about 50 variables, most just 1-3 words). Does this sound reasonable for a relatively high traffic site? If I don't do this, then many of those variables will probably be queried from a database more than once during a visit, which seems unnecessary when I can use session variables. Are there any guidelines on the performance penalty for using large numbers of session variables? Or is the affect so minute that I really shouldn't worry about it? (especially compared to querying a database) Thanks, Andrew