Unity 2D Collider Safe Sizes

Does anyone know what sizes are safe for the 2D Colliders? For example, the minimum and maximum radius of a circle collider or the min/max x/y size values of a box collider before they start to act up due to rounding errors and other "fun" floating point issues?

I wanted to have everything normalized to around 1 unit of size.. however... the default camera is set up such that to make a character fit within it, the average size of a player (in a top down game, using a circle collider) would be about .4, with sword-like weapons having box collider values like (0.096, 1.68)

I'm a bit worried that this is two small.

Any advice?