James Gasik
We don't talk about Pun-Pun
Level limits kick in for Halflings starting at level 8, unless your DM uses the optional rule where high ability scores let you exceed your cap. Gnomes only go up to 9 as Clerics. Just about everything else is a minimum of level 12, I want to say, which means you're probably fine.
Hit points will be a mess, but if you're a Cleric/Thief or Fighter/Thief, I think they should catch up, depending on how your group calculates them. I use fractional hit points, so if you go up a level of Fighter and you get half a d10 and you roll a 9, I'll have you note you actually got 4.5 hit points at that level. Just so you don't get math screwed by rounding everything down.
Other DM's may not do this! I've run into some contention about how bonus hit points from Constitution should be handled- some of the DM's I've talked to have had very restrictive systems because they thing multiclassed characters are too good.
If you have the ability scores for it, another option is dual-classing. A few levels of Fighter to get stronger hit point totals, then switch to Thief. It will still take you awhile to get useful, but you'll be more likely to survive.
Hit points will be a mess, but if you're a Cleric/Thief or Fighter/Thief, I think they should catch up, depending on how your group calculates them. I use fractional hit points, so if you go up a level of Fighter and you get half a d10 and you roll a 9, I'll have you note you actually got 4.5 hit points at that level. Just so you don't get math screwed by rounding everything down.
Other DM's may not do this! I've run into some contention about how bonus hit points from Constitution should be handled- some of the DM's I've talked to have had very restrictive systems because they thing multiclassed characters are too good.
If you have the ability scores for it, another option is dual-classing. A few levels of Fighter to get stronger hit point totals, then switch to Thief. It will still take you awhile to get useful, but you'll be more likely to survive.