You can do as many leves as you want up to 99 maximum, you aren't restricted in how many you undertake, so long as you've accrued the leve allowance to do them - however the number of leves allowances accrues gradually.

It would be a leve spam fest if leves weren't an 'allowance'.

Budget wisely ^^

I've left all mine to do when I have a job at a higher level and can earn more from doing them. My leve budget hit 98 last server update, so I'll have to get some done within the next few hours or they'll go to waste...