Transitional planes like yours are pretty easy to get working again and a bit harder to get looking like new.
For a first go, I wouldn’t do any more than necessary for good function. A few scratches are no big deal, but if they affect use or the bottom isn’t flat, they need to go. Often a card scraper used judiciously is all that is required.
As Dave says, any removal of material in the sole will open up the mouth, which if you will use the plane as a scrub plane, is fine. If, on the other hand, you want a plane for finer work, you need to plan ahead. There are three basic methods to close a mouth.
If a plane is far gone, you can remove some stock to get the sole flat, add a thin sole and re-mortise the mouth. This is last resort, as it affects the looks the most. You want to have the plane the same thickness as a new plane.
A less open mouth might profit from the addition of a “Dutchman” at the front let into the sole and glued with a reversible glue like hide glue.
And a third method is to add a thin shim behind the iron to close the mouth up.
Any repairs should match the original beech, , and should probably be followed by an oil like linseed or walnut oil and beeswax, or tallow and beeswax, which will darken beech to look older the quickest.
The iron bits are standard plane restoration. They can be cleaned with a standard deruster as Dave mentions ( I use citric acid baths most often) and OOOO steel wool in the tough areas. Then use a metal polish on the irons if you wish. If the japanned parts have lost their finish, just oil or wax or strip and paint or re Japan to taste. (Google Pontypool for a japanning product, use Ford Engine black spray for paint)
Just don’t be too worried about any collector value. There are still scads of these out there, and the market isn’t strong for them. It’s even probably OK to cut the plane if you want a shorter one. You wouldn’t be the first to do so. Just get the proportions right. Most of the transitional planes used the same metal parts.