How do I cut a new crawlspace access in a brick foundation?
I think this deserves to have an engineer take a look and give you an opinion. Removing a large portion of the foundation is not something you want to mess with without a plan. Plus if you're going to bother to do it, you might as well make it a real door so that you can actually get boxes in there or something.

As an alternative idea, it might be easier to put a trap door in your floor somewhere above the crawlspace at a convenient location. Obviously this has its own structural considerations, but it might be easier and would let you avoid messing with the foundation.