HI Jonny!
Nice looking boat, if it's in as good a shape as it looks, then definitely worth the $1900(ish). I'm assuming you have physical access to the boat, you'll want to check for soft spots on the hull, any bubbling (osmosis), horrendous cracks, etc. The trailer is a "freebie", it's just about worthless, so I'd be ecstatic that the owner is repacking the hubs for me (it's an easy, but nasty job). As usual, I'll give you my thoughts in no particular order:
-Most of your questions and concerns have been discussed already on this forum. Unfortunately, the forum search function is not as robust as it could be

. No problem, use google. Search for: site:http://forum.daysailer.org +"SEARCH TERM 1" +"SEARCH TERM 2"..... etc. For instance, try that for "asking price" and you'll find a few discussions about what to pay on a boat.
-Speaking of price, in my "life experience," you can usually haggle 5% off a private asking price with no problem, and 10% with some work. More than 10% off is rare. At the end of the day, price negotiations are about EGO - you have a price in mind where you'd feel like a fool if you pay more than that, the seller has a price in mind where they'd feel like a fool if they accept less. You have to set your own ego aside and then gently deflate their ego. It works a lot better if you approach the negotiation as a partnership - "You want to sell a boat without a lot of aggravation, I want to buy a boat without a lot of aggravation, let's work together." I usually just say "I really like this boat/car/thing I don't really need, but the price is a bit of a stretch for me, what's the lowest your willing to go?" And they knock off 5%. If I'm willing to walk away, I counter with 10% off, otherwise I just take it. Of course, the first step is KNOW YOUR BUDGET. Good Luck!
-I think those are Intensity Sails:
https://www.intensitysails.com/gesaforda.html Same windows, and they come stock with one row of reef points. If they are in fact new (they'll be stiff/make a crinkly sound), then they're worth $500. So you're buyer is really asking $1400 for the boat, which is reasonable. On most used boats, the sails also are a "freebie" as you'll have to replace them soon enough.
-Make sure the boat and the trailer are titled and licensed! Getting new papers for an old boat and trailer is a major pain in the can. It's doable, but will eat up your time, patience, and faith in humanity.
-Trailer fixup - buy/borrow/steal yourself an angle grinder (and good gloves!) and get a wire brush attachment, clean off the rust, then spray on a few coats of rustoleum. Good as new! Check and/or replace the wiring and lights. Get new rims+tires, and get a spare tire while you're at it (this goes for about $100/wheel with shipping). Done. We've discussed the finer points of trailer repair before, but you just want to make sure the lights light up correctly, there are no obvious weaknesses in the frame, and that the wheels turn without "catching" or making any horrendous noises. Oh, and if the trailer has leaf springs, they shouldn't be broken/look like they're about to break.
-Trailer bunkers are a whole other story. From what I can see in the photos, those are terrible - they concentrate stresses on single points. You want long, wide boards going fore and aft, covered with some indoor/outdoor carpet. We can discuss in more detail some other time, but when you are checking out the boat, make sure to inspect the hull closely around the contact points between boat and trailer. Are there any cracks? do they look deep? How badly does the hull flex? It's all repairable (even cracks that go deep), but it's a negotiating point for price.
-EP Carry - yeah, they're expensive, mine was twice what I paid for the boat itself. Worth it for ME because of the convenience. As GreenLake points out, trolling motor is fine, paddle is fine, used outboard is fine. Look at
https://www.searchallcraigslist.org/. It's all about tradeoffs, and again, we've discussed it quite a bit on this forum. Whatever you do, you can always upgrade later. Don't overthink it, you're buying a sailboat, not a motorboat.
-Learning to sail - the essential skill is knowing from which direction the wind is coming, the trimming (setting) your sails accordingly. When I was learning, I used to "sail" myself as I was walking - I'd pay attention to the wind, then imagine how I'd be setting my sails. If there was no-one around, I'd even "tack" upwind! Sailing is 90% mental (and you have to be crazy). Bottom line, just get out there and sail.
-That being said, on the DS an extra person really DOES help. If nothing else, as added weight to make the boat more manageable. Anyone who will listen when you say "please sit there,now please move over there" is perfect. Basically, you want them to sit on either side of the thwart (plank going across the middle), facing inwards towards the centerline. Have them sit on teh upwind (high) side and move over to the other side when you tack. That's it!
-Again, search this forum for more solo sailing tips. Holding both sheets in hand (or at least them main) and not cleating them down is crucial. That allows you to "ease-hike-trim" as Gl explains in his guide.
Man, I love that yellow hull!
Best,
Tom