Can I fill the balloons with yogurt?

I wouldn't fill a tank prior to storing because of the expansion and contraction of the gases. It's best to simply leave it empty or half full.

If you are preparing tzatziki, greek yoghurt is good. Plain yoghurt has to be drained for liquid before making tzatziki.

Yes, you definitely can add maca powder to yogurt. Start adding it to plain yogurt to make sure it tastes good. After you know you like the taste, you can...

Yes, oat bran can be used as a topping on yogurt. It does not need to be cooked to be used as a garnish.

Yes. You can use a bucket, a jug, or (if it's nearby) a handheld shower-head.

With tortillas, you can generally fill them with anything you want/think will taste good. Have fun with different flavors, don't feel limited.

You can worm her with the yogurt, just make sure to watch her for 24 hours to make sure she is okay.

Yes. They are meant to be spliced together.

Yes, if you fill it too high, the slugs can simply drink it. Fill it up about 3/4, and you should be okay!

Personal opinion, I'd say the fuller the better. Skim milk might make it watery rather than viscous.