What are all the rewards for leveling up?
With the daily challenge system, players can earn XP for each type (except colorless), 5 XP grant a level up.
There are visible rewards for each type (Coin for Level 1, Sleeves Level 2, Deck Box Level 3), as well as other rewards for the total level.
I was able to determine that Level 3 grants a choice of 2 daily challenges each day instead of just one random one. Also, reaching Level 5 unlocks a second slot to store challenges so I don't have to complete one each day, but can wait a day. I found this post, explaining that the following rewards are currently being awarded:
- Level 3: Pick from 2 challenges each day
- Level 5: Store up to 2 challenges
- Level 8: Pick from 3 challenges each day
- Level 10: Store up to 3 challenges
Are these all rewards or is there more reason (except for the rewards for completing a challenge themselves) to level up past level 10?
The player level decides which challenges will appear for you to select each day. Higher levels increase the reward you receive and give you greater chances to be presented with Rare rarity challenges which give you access to booster packs.
The most important level up threshold is Level 16. At this level and beyond, the booster packs you receive from Rare Daily Challenges are unlocked and can be traded. As the trade economy uses booster packs as a form of currency these are incredibly important for obtaining the cards you want for decks you wish to create.
I'm not aware of any other rewards beyond the ones you mentioned and the level Daily Challenge booster packs start being unlocked ones.