I would've loved that as a kid. For that matter, I did actually fill some balloons with hydrogen using vinegar and something (might've cut some magnesium off one of those primitive fire starters, or I might've used a weaker metal, can't quite remember). I think I used the glass tube Costco used to use as a vanilla bean container to strap the balloon onto.

If by "much stronger" you mean "less than 10% stronger"

A theoretical "vacuum filled" balloon would only be 16% more lift per unit volume than a helium balloon.