Tooth still kinda grey after root canal with internal bleaching. Should I get a crown/ veneer to match the tooth to the others?

It would be acceptable to place a new temporary on the tooth at this point.  However, the final restoration, as you have been told, would need to wait until all healing has occurred, to make sure that the gum tissue does not change. 

I am sure that your dentist will make your permanent crown fit you teeth properly without a gap.  Let them know of your concern and they will take good care of you and give you a nice result.  Good luck!

Your best bet is to Redo the Dental crown and use a dental laboratory that does custom work.However, If for some unknown reason, you must keep the crown and do not want to remove it,You can also prepare the crown, as a veneer preparation, at this time, take an impression and order a customized...

Depending on how much of it is broken and what type of crown it is, it may be possible to repair it,at least temporarily, with composite bonding. The best and longest lasting solution is to have a new crown done unless you absolutely cannot afford to. Your dentist can give you the options...

I would have  conversation with your dentist and explain why you were unable to get back in to have the crown seated and that you have paid for it and would like to work out a way to get it finished. It sounds like the dentist may not have the crown any longer, so a new impression would...

Yes, a crown can last 30 years depending on many factors including how clean you keep it, your biting habits, the type of material it was made out of, the skill of the dentist and lab,etc. If you do not take care of your crown, you can get decay at the edges of it that then can work its way up...