Buying my first Jimny

It's very difficult to comment accurately on rust without actually having a poke at the rusty areas to see how bad it actually is.
As a Jimny goes I've seen a lot worse than this, but also better.
From the photos it looks like the rear body mounts are on the way out, worth a closer look in this area. The jack / floor area it's hard to see if it's surface rust, again worth a second look incase it's rotten, it's a common failure point.
The rest just looks like standard Jimny surface rust.
It's going to need some rust prevention or even welded repairs soon, so try to factor this in if you purchase.
As for the oil leak it's possible this is just oil that gets dumped down the side of the engine when you change the oil filter, it tends to run around the sump gasket in this area unless you clean it up. That's my assumption, or it a leak!
Just my personal, none professional opinion based on photographs. If you are unsure of it's condition it may be worth getting a professional opinion locally.
Good luck 
Mike