Realistically, you shouldn't have to replace any of it. If it were me, I don't think I'd be overly worried about it ... wouldn't bother me a bit.
However, you are not me, so to answer your question ... you don't need to replace it to get it cleaned up. You'd just need to pull the pan down, clean the rust off of it, then put it all back together. You'd need a replacement gasket for the pan (between the pan and the block) as far as parts go. A Scotchbrite pad, a bottle of acetone, some rags, a spray can (rattle can) of engine enamel primer, & a spray can of black engine enamel.
Take it down, de-rustify it, clean it up, prime it, then paint. I'd have no fear of the bolts, as just the heads (not the threads) which are rusty ... you should be able to pull those off without an issue. You can clean the heads up on those, stick the threaded section through some card board and paint them the same time you're painting the pan (with primer, then paint). Really, it's just that easy. When replacing the bolts, ensure you're not over tightening them ... just past snug (probably about 15-18 lb-ft of torque, as a guess). You want to get them even, though, so as to not warp your freshly painted oil pan. Also, while you're at it, if there's a gasket on the drain plug, you might want to get a replacement for it as well ... looks like it might be seeping a bit.