Hydrogenation at atmospheric pressure in amateur environment
I've adddressed a part of your question here.

As far as the catalyst is concerned, 3-5% Pd/C is fine. 


  What is an effective method for generating the hydrogen to fill the balloon with? I suppose that normally a pressurized hydrogen tank would be used for this, but I find this overkill for the reaction I'm planning. Furthermore, the use of pressurized hydrogen tanks is not quite without danger and I'm not trained to handle them safely.


In the lab, I only used pressurized tanks. While commercial hydrogen generators are available - they are mostly used to generate hydrogen gas as a carrier gas for GC/MS - these things cost a fortune and really would be overkill.

Actually, pressurized tanks are pretty safe if you follow some rules: 


Obviously, you can't attach the pressure regulator and operate the whole thing unless the steel cap over the main valve is removed. Don't start anything unless the tank is secured to the lab bench or the wall with a clamp, a chain or another sturdy contraption that prevents the tank from falling over! You want hydrogenation, not a rocket ;)
Get familiar with the pressure regulator.
When you're done, remove the regulator again and put the cap over the main valve. Keep the regulator at a dry and clean place. 
No grease on the threads!  


When operated with a bit of common sense, a small pressurized tank is the most convenient option.


  What is the function of Celite when filtering the catalyst?


When you filter off the catalyst, you'll typically use a suction filter with a base of sintered glass (fritted glass). Palladium on charcoal is a very fine powder that will clog the fritted glass. A pad of Celite in the suction will prevent this. Celite is cheap, suction filters are not!