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Can't really see a lot of detail but nothing there looks out of the ordinary.
Oily rag to clean the fork and slather a bit of grease on the steerer and work it into the threads. Seatposts usually look like that when they've been on the bike with no grease down the seat tube. Again, just wipe it down with an oily rag. Poke the same oily rag down the seat tube with a screwdriver and work it round and up and down a few times to clean it out, then just wipe a bit of grease down the tube. This will stop it seizing in and stop it rusting.
You could spray a bit of Waxoyl or similar down the tubes to protect the insides from rusting, but I've found it all runs out when it gets hot in the summer. It runs down into the bottom bracket shell and drips out through the bearings - which isn't ideal.
What is the strat vs this rust. Seller assures me its surface level only, but I guess time will tell. Was a cheap frame and is destined for a hard life so I'm not too picky, but would like to have a go at cleaning up at least the forks + frame before putting them together.