Most modern browsers will integrate spell check for you, Firefox for instance, will do it.
I think adding HTML Editor would work ok, but one thing to keep in mind is javascript is used quite heavily in the admin to save the titles and descriptions. If you make sure to keep the "edit_title" and "edit_description" id's that it might work. I haven't integrated HTML editor in PowerGallery, so I can't say 100% that it will work without some decent tweaks to the code.
The other thing to keep in mind is you might need to adjust the database fields to be "text" columns to allow for the increase in characters you will be saving for the title/descriptions.
-justin