I heard the leveling cap is 81. Does that mean from there I won't be able to increase my health, magicka or stamina from then on?
As of Patch 1.9 of Skyrim, a level 100 skill can be made legendary, resetting the skill to 15 and refunding perks spent in the skill. A legendary skill can be leveled again, which will result in more perk points. This can be done for each skill as many times as you want with as many skills as you want. It is theoretically possible to get all the perks in the game and have a huge pool of Magicka, Stamina, and Health.
More details can be found here: