General

Make sure to get the first star with AEE as it is 100%. You should be able to on average. If you get back to 0 stars, make sure to AEE back your 1 star.

Probably; yes.
These charts/graphs are credited to @cb000

For Superior Equipment:
Graph of Cumulative Costs: http://imgur.com/WTrmh09
Chart of Numerical Data: http://imgur.com/iGvycGS

In essence, what you can pull from this data is that, on average, 5-Staring an equip will cost ~1.5 Bil.
So, if RNG is with you, 5b should be enough to pull off 5-Staring two Tyrant pieces.

I spent 12b on my shoes for them to go back to 0 stars.

It's all luck.

It depends how lucky you are. You can end back 0 stars who knows? Go and find out yourself.
Or get yourself a 5 star AEE and use Guard Scroll.

I wish the "it's all luck" goes through people's heads.