Are there any copyright issues in the case of creating a MOC based on a Lego Technic set, and then publishing my own instruction and/or video for it?
I think the key here is if you are trying to profit from it. If you are doing this as a hobby, aka for fun, you have nothing to worry about. If you are trying to sell the model and/or instructions, then you risk a friendly "Cease and Desist" letter from the Lego Group.
Here is a paragraph from their "Fair Play Brochure":
"For this reason, certain guidelines have been developed to outline the proper use of the LEGO Group’s trademarks and copyrighted material for non-commercial purposes in domain names and websites. The LEGO Group’s trademarks and copyrighted material may NEVER be used by unrelated third parties for their own commercial or marketing purposes, unless formal permission or a written licence has been granted by the LEGO Group."
I see this sort of thing done regularly and never heard of anyone being shut down. Even really famous builders like JKBrickworks publish modifications for official sets and he would definitely be on Lego's radar having had two sets created through the Ideas program.