um... sensors wouldn't be able to detect what sort of systems are on a ship. Sure, it might detect an active shield and maybe, for an expert, a vague idea of shield strength, but it would not be able to detect inactive systems, or for that matter their make. There's no way they would be able to detect the presence of most Asgard systems.

and since when is a 700x650x315m ship same size as a 225x95x75m ship?

Modifying a tel'tak with weapons is tricky. Possible, but tricky. Probably some reason the goa'uld didn't do it long ago. But still, that's not too much to worry about. its the above that is illogical.

No idea if rings are detectable, but they probably are. Shields, at least ori-class, block rings, though. No idea about whether asgard shields block it. 

Shoot first, don't ask questions is a nice policy in reference to the scout.