General

Reason why the RA/Tyrant sets are top-tier is due to 1) Their enhance/scrolling values and 2) Top/bottom allows you to cube for more %stat.
To "maximise" your range, it's best to get a balance of %stat and atk items (this goes for other classes).

Just sayin' in case you want to blow billions on equips you don't plan to cube, yet gain the same amount of range by just getting other decent (much cheaper) equipment without spending as much.

This isnt very clear so assuming everything is clean except weapon, it would be less than 100k.

I would say 80k~100k

Depends on %dex on accessories, stars on tyrants, and link skills, but I would assume around 60-70k at level 150.