I don't see anything wrong with this, as long as the achievements are well programmed and not using precious resources because a infinite loop is needed.
Like this one:
Colorful Canvas - Paint a lot of bricks
This needs to check every time a brick is painted, which can be a lot when using the fillcan making it lag even more.
Here are a couple more ideas:
Changing the game - Install a custom addon
Getting social - installing RTB
Educational - Completing the tutorial
Games! Games! Games! - creating a minigame
Being popular - host a server with 30 players
(maybe even show your highes amount in a leaderboard)