Very new to the Delica world, but it sure doesn't take long to get hooked, does it?

We looked at our first potential purchase today. It recently had the engine and alternator rebuilt, plus the transmission, timing built and glow plugs were just replaced. Interior is clean and in great condition.
The problem is there's quite a bit of rust – particularly the underside seems covered. There's bits around the rest of it: a big chunk on the front bumper, some starting on a wheel well, and on the centre of the rims.



This is my first time getting a used car, and with this one being so old (1991) I'm not sure if this is to be expected, and if it can be fixed up. The rebuilt engine should last quite a while, but if it's just going to rust out, that would be sad.
Is this worth taking to a mechanic for a good once over? Or is it a lost cause?
I'd really appreciate any advice you all could offer. Thanks so much in advance! This is an awesome community, I'm so glad to have found it

Lauren :)