Pressure at 30 km is very low - too low for many pressure sensors. Keep that in mind when looking for a suitable sensor! Same for the temperature, it's pretty cold along the way, check what to expect and choose your sensor wisely.
And indeed find someone experienced in launching such balloons, and who also knows about where/when this is allowed. You don't want to risk hitting a passing plane, no matter how small this risk.
Recovering your kit may be one of the hardest parts of this project indeed, keep national borders in mind as well when planning your launch and where it may end up.