First time brewing - some concerns and questions

well 2 days ago i made my first ever batch (just a simple hefeweizen from extract with white labs hefeweizen yeast). This morning i saw first bubbles in the air lock.

Now i am worried about the whole thing exploding. How likely that i will have a mess on my hands when i will come home?

Also for hefeweizen is secondary fermentation necessary? Or should i just bottle it straight from the primary? The instructions in the kit i got are very unclear about that.

Hefe's ferment aggressively. Are you using an airlock or a blowoff tube? If you're using a regular airlock, you may get some krausen in there and worst case scenario, it may blow off. If it does, it may create a mess, but the layer of CO2 over the beer will keep the oxygen away. Look into getting a blowoff tube for your next hefe batch.

You don't need to secondary hefeweizens. Racking to secondary usually means a clearer beer, which is unnecessary with hefeweizens since they are cloudy anyway. Just leave it in your primary for 2 weeks, bottle, and allow to condition for 2 weeks.

You might! Next time use a 1" diameter "blow off" hose instead of the airlock for the primary fermentation. Put the other end in a bowl of sanitizer solution.

Racking off to a secondary fermentation vessel is never necessary, just strongly suggested. I would rack off the settlement once it is clear that the fermentation is slowing down... like 2-3 days or so; you don't need to wait for the head to fall back into the beer (in fact it is suggested you do not wait). Be careful not to splash it around.

Assuming it is a 5 gallon batch... What size is your fermenter? As posted above airlock or blowoff?

Personally speaking no secondary clearing vessel is necessary for ales at least. Leave it about 3 weeks and bottle or keg. If you have you are worried about it blowing, even in a 6-6.5 gallon ferementer (which could happen with a hef) Stuff a piece of 4' 1.25 OD tubing in there. the other end in a bcket of sanitizer and worry no more. When the kraeusen settles down return the stopper and airlock.

I wouldn't worry about a secondary for a Hefe, especially your first brew. Just let it sit for 2-3 weeks then bottle.

well so far there was no blowover incidents. The fermentation is going at a very tame and consistent pace.

As far as i understand the secondary fermentation is for making beer more clear, which is not the case in hefeweizens. Why do some recipes call for secondary then?