I'm going to say if the spider is still stuck then its most proberly dead.
I been keeping spiders for 4 years now, and I have only lost 1 spiders to it getting stuck in a moult.
SO no its not a common occurance but it does happen from time to time. its all part of the hobby!!
II lost a B vagans female that I had for 3.5years she just died for now reason!
once a week is fine you can also add a water dish if you really get worried.
I mist my slings once week in summer and maybe every 2 weeks in winter, reason is the heating pad cause condensation, so if you add to much water the substrate becomes water logged and the spider will not be to happy. but if I feel they need water I mist them when ever! Allot of my larger tarantulas have water dishes.
but at the end of the day you will learn what is best for your Pet tarantula and what you feel is the best approach.
Ja the expo is on this weekend.
diffently worth a vist and you can meet a couple of nice guys who are also in the hobby of tarantulas,some times you find some really nice priceed slings, but you can also purchase tarantulas from these sites. A bit cheaper some times. I have dealt with all of them before.
www.petbugs.co.za nice selection of tarantulas. trustworthy and very nice guy to deal with.
www.the-spider-shop also trustworthy and nice guy to deal with.
www.tarantulas.co.za there is often tarantulas for sale on this site.
www.tarantula4sale.co.za trustworthy.
www.tarantulatrader.co.za. trustworthy
And they also can get posted to you!