Hi, quick rules question:

Example: If running the MC80 Battle Cruiser with HTT and X17, do both upgrade card effects happen when using your first attack against another ship, if the defender spends both a Brace and Redirect? Or, does it work like critical effects, where you can only resolve one effect per attack?

Also, upgrade cards that affect defense tokens without the text reading "...a ship" can be used against squadrons with defense tokens, correct?

thanks in advance!

Correct that multiple upgrades stack, barring some other specific reason that they shouldn't (the one crit per attack limitation, for example).

And yes, things like Intel Officer and Avenger work against squadrons with defense tokens.

Both effects trigger.
If the opponent is using a brace and redirect token, you can only redirect 1 damage and the brace only reduce the damage by 1.
So it is not really smart to use any other defense token against the HTT when you want to use brace.

Abut the second question: Yes. As long as it is not reduced to ship it does affect squadrons as well (Intel Officer for example).