Can't Preview deal with many photos?
To the best of my knowledge there is no documented limit to the number of photos you could open at one time using Preview. Usually, when software has no hard-coded limit, the only limitation is that created by the amount of RAM available to the application.

In the case of Preview, the more RAM available the more it can take advantage of when opening images. In addition to RAM being a factor, the number of images Preview can open at once also depends on the image format and the individual image sizes.

You don't specify how much RAM you have and what else (if anything) you were running at the time, nor do you specify the exact model of MBP etc. However, I've been using Preview for over 16 years and can attest to the fact that in some cases it's only been able to open a few hundred images, while in other cases it's been able to open 1000s.

My suggestion would be to start with only opening a hundred at a time and if it handles that without problems, double it to 200 and so on. You'll soon establish what's comfortable in your scenario.

A final word

One thing to consider also is that if you happen to have a corrupted image file then this could cause problems. I've seen Preview (and other apps) normally capable of opening a large number of files, randomly crash because one of the files you're trying to open is damaged in some way. Likewise, similar problems can be experienced if you've inadvertently selected a file that isn't supported. While these issues aren't usually a problem as Preview would just present you with an error message, it can be a problem if Preview is processing a large number of images simultaneously and is also waiting for a response from the user.