Most sets (and most computer instantiations) have ships of 5,4,3,3,2 made up to look like carrier, battleship, cruiser, submarine, destroyer

I don't think limiting speed and direction of movement is viable - the movement is needed because reducing field of fire means you don't cover the whole board and thus can't find the enemy. Slow movement such as you suggest does nothing to alleviate this.

I think that having a small number of mobile ships with a very small fire radius is better than an n turn penalty - it means that you can move it, but as soon as you *use* it, you're vulnerable.