Thinking about putting steam on my system but don't want it interfering with Galaxy, is it likely to cause any problems or conflicts ?

I haven't had any issues whatsoever...

... and...

Galaxy can connect to Steam and start Steam games through the Steam Client. So I wouldn't expect much of an issue.

Just got seriously distracted on the Blizzard site with Starcraft 2, Wicked !

did notice some lag between the steam and galaxy acces. No acces to games installed for example or other stuff happening such as missing achievements or no game hour registration

I would avoid getting moisture of any kind near your system. In the great scheme of things though, it’s unlikely to affect the galaxy.