No reason not to - I suppose there might be an upper limit to how many creatives are allowed in one account but I've never seen it.It's a good practice to have a few for testing, keep an eye on them, eliminate the ones that don't perform , and keep trying out new variations of the one that do to see if they can improve. The only problem I can see is that if you create too many at once you just won't get them rotated often enough to get meaningful feedback.
Exactly the more you have the longer it will take to get meaningful data. So you would need to wait quite a while to get good data on 10 ads versus less time for data on 2.
Test only two or three at a time, not "lots and lots". No meaningful data will come of it and the poor performers will hurt you and you may not even know it.