welcome.
glad to hear you got the car you really wanted.
get the rust fixed as soon as you can, and stop it spreading.
the other 2 items are easy fixed.
post pics when you can.
hope you enjoy the forum
so long as its done right, its ok.
think about it, theyre welded from factory.
a proper weld is actually stronger than the steel surrounding it.
and its only if the cracks are LESS than 150mm long.