Users have recently discovered the saved map file limit in Halo 5 is 40 (proof here). Furthermore, I went ahead and downloaded a bunch of random maps from friends to my bookmarks and discovered that the bookmarked map limit is 100, which appears to be unaffected by the amount of saved maps you have. Saved gametypes and bookmarked gametype limits also appear to be unaffected by both map limits and vice-versa.
Just a little heads up for anybody out there or for anybody potentially having trouble saving maps.
Just a little heads up for anybody out there or for anybody potentially having trouble saving maps.