by 5 tag limit i mean that your posts will show up in the tags of the first five things you tag it as, but not any others 

so if i tagged something voltron, keith, matt, pidge, shiro, lance, and hunk, my post will appear in the first five tracked tags, but not lance or hunk- only the first five are searchable

…unless of course tumblr has changed things again

but when it comes to hard limits im pretty sure a post cuts you off at 30 tags but ive never put that many so i dont know first-hand