Maximum number of apps we can publish?

Regardless of whether there is a ceiling or not (I'm not 100% sure), 70 apps shouldn't be a problem. Disney, for example, has published almost 100.

Now, there is a ceiling on the number of test iOS devices you can link to your account, so that's where you might have heard that.

I'm not aware of a currently published/official limit, but when some devs were pushing 900 a fear years back, Apple began pushing back. App Review may decide case-by-case, but since the store is a black box, the avg. dev is left to imagine where the line is.

I think you'd have to go well beyond 70 to cross the line, however.

Interesting to note, perhaps, that cramming doesn't seem to be one of the top reasons for rejection: https://developer.apple.com/app-store/review/rejections/