Can I use NFL players nicknames on a shirt?

The use of "names" suggests endorsement and the "names" are a part of the teams sales promotion and will create consumer confusion. See IP Counsel.

Can I share, via SoundCloud, recordings of our non-profit band performing other's work?

No. The "reason" is irrelevant. The use is copyright infringing. You will be subject to Infringement Litigation. See IP Counsel.

Can I redesign a bands poster without their permission?

Use of parts of original artwork will be infringement. Use of your work derived from original artwork from other bands will be infringing as...

Is it fair use to make a video of a teacher using copyrighted images/flashcards for a non-profit ESL video?

Fair Use is a defense asserted once the user has been sued for infringement. Does the Fair Use comment or criticism or is it used for teaching or...

Can I Iegally sell a personalized letter from a Disney character ?

Yes, write a letter and sign by Santa Clause or Mickey Mouse. But not if you decide your Hit Girl letter is to be sold and widely distributed. ...

What are the terms of service? Updates are frequent on many products which may reduce potential of being hacked. See IP Counsel.

Fraud nn the Patent Office. Call PTO Legal dept re: who has standing to raise the question. See IP Counsel.

Will an unregistered trade mark have claim over a register trade mark, registered later?

First, see UK IP Counsel for guidance. In the US - "will registration of a different name than one that is used but unregistered but popular be...

See IP Counsel. The attorney will know what you need and what you don't want to say. See Counsel

Copyright - do I need to get copyright owner approval to use an ad or photo for a well known brand in a marketing book?

Yes, you need permission in that your use is not Fair Use. See IP Counsel.