Thinking of only leveling up when I kill a dragon... seems like that would be a good time to level right? I realize I may have many stored levels at those times but I’l looking for interesting ways in making the game more challenging...

FYI I only play on Master and no I do not grind Smithing or Enchanting.

Banking level ups will actually make the game easier. You will be facing stale enemies, while your skill levels continue to rise. Leveling up as soon as you are able, will increase the level of the enemies as well as the level of the Dragons.

Granted you will not be using perks, but I bank those anyway. So leveling up but not spending perk points will give the better challenge.

If you're doing this for roleplaying reasons I think this could be a very unique and interesting way to level a character. It seems to me that this approach would add a lot of extra significance to defeating dragons.

But if you want to add difficulty to the game, Senor Cinco is right. You'll be shooting yourself in the foot.