I am looking for tips on the best way to stuff a bigger balloon with 5in balloons using helium :-)

There are videos on Youtube.
Basically, put some helium in the big balloon.
Put a 5" balloon in the big balloon using a chop stick, or similar, and line up the nozzles.
Inflate the 5". Pull the 5" to block the helium escaping from the big balloon.
Tie the 5". Push the 5" into the big balloon, using another 5" on a chop stick, and repeat.
Repeat until you have enough 5" balloons, then fill the big balloon.
Use helium in all balloons. You can't mix gases.