Sorry for the late response, I had a busy night last night.
Unfortunately, the Sunline FW's are rare, especially the 18' models. I'm assuming you probably have the rear-dinette F-1850. If you have a rear kitchen, then you'll have an 1860, which I have no pictures of.
I only have pictures of one 1850:
This one is #1344:
Unfortunately 1344 is missing the original hubcaps. The originals would have looked like this:
I'm guessing this is the manual you found?:
I remember you mentioned something about missing a rock guard for your front window. Ironically this example is missing it too...maybe it's the same coach? Here's an example of a rock guard if you wanted to make one up. This happens to be a rear one, but in this case the striping cut is the same as the front. For those members who have attended the Buttonwood Meet & Greet, you probably will recognize these next couple pics.
To answer your first four of five questions:
1) I'm not sure when Sunline started building your model because I don't have all the brochures going all the way back. However there is evidence that it was built all the way back to 1982 when they went under a different model number. At the time, it was an 18 1/2' RD Fifth Wheel. They produced the F-1850 through the 1989 model year.
2) Original MSRP list price was $8,326.00 Of course that doesn't include any options at all, so you'd have to add in those. It's hard to say what the options would have cost new...they only way to really tell that is to have an original sales contract.
3) Standard Equipment should be listed in the brochure.
4) I do remember options in 1985 are listed on the very last page (the back) of the brochure. You can see what ones it has. Keep in mind that some things may have been added in the aftermarket and some may have even been removed. This especially applies to spare tire covers. Most of them have deteriorated these days, so people take them off and replace them with plain ones. There were other options not listed that were more custom things that people had added on. It's possible you have some of these too. One that comes to mind is a rock guard for the rear window. I'm not sure if it was ever mentioned in the brochures, if it was it wasn't very often, but from time to time I see them show up.
Hope that answered all your questions. If you have any more, don't hesitate to ask.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR