What you see is what you get! It's just an opportunity for players in the match to commend each other on good gameplay. :)
_{@PlayOverwatch on Twitter (May 30, 2016)}

Cards can reach "Epic" or "Legendary" status at 5 or 10 votes respectively. The only 'reward' is a unique voice line from the hero on the card. There's a full list of commendation voice lines on the Overwatch Wiki.

In other words, commendation votes are like clapping. They do not have any long-term tangible impact.

There is no level cap.

There is a level exp cap, that scales until you hit level 20:

As of a recent update, every level past level 20 now only requires 20,000 exp to reach the next rank, and this is consistent even after "prestiging". So once you hit Level 100, then reset back to level 1, but with a new prestige border icon, you will still need 20k exp to get to the next level, and so on.

New portrait borders are given every 10 levels, starting at 1, 11, 21, 31, etc.

After you hit level 100, you "prestige" and reset your level to 1, but gain a new portrait border. This happens every time you hit level 100 again.

At level 1890, or approximately your 18th "prestige" and at level 90, you will finally gain the last portrait border which appears gold and although you can continue prestiging over and over again your profile border will no longer change.