Greetings to you and welcome aboard!
I have the identical boat to you: Same boat, same engine, same year. Judging just by that one photo, it looks you you have a very clean specimen of an E26. They are a fun boat to sail and have a remarkable interior for a 26 footer.
To offer a bit of perspective, owning any boat, particularly one that is 36 years old, is a maintenance-intensive deal. It just goes with the territory. You will gain more confidence and skills as you work through different issues. There are some really knowledgeable people on this forum who will be happy to offer you some help.
None of the issues you have presented are especially alarming, but you will need to tend to them. All boats this age have issue, and no sooner do you fix one issue than something else crops up. But eventually you will get the boat in pretty good shape overall and it does get better. Usually. Mostly. Sometimes.
Leaking hardware is an issue to which you will need to attend from time to time. While Ericsons are decent boats generally, it is also true that from time to time the factory did some pretty goofy things. The aft starboard leg of the bow pulpit on the E26 is Exhibit A. Here you've got the leg of the pulpit going into a socket affixed to the deck with wiring running right through the pulpit leg and then straight through the deck with no serious attempt at sealing it. Any water that finds its way between the pulpit leg and the socket--which isn't even close to water tight--is going to migrate through the deck and in between the deck and the headliner. This was a supremely stupid design decision, to put it mildly.
What I did--which may or may not be the ideal repair--is to use a silicone (I believe) self-annealing tape to wrap the joint where the pulpit leg goes into that socket. I also inspect the tape from time to time just to make sure it hasn't developed any tears or anything. I also rebedded both of the pulpit sockets where they attach to the deck. You can use either a polysulfide caulking to do this or, as some people prefer, butyl tape. There's lots of into on good techniques for doing this, and people on this forum can help you with the details. At that point you will have taken care of the main points water ingress as far as the pulpit is concerned. (The forward legs, should they leak at all, do not go into wood core and would simply dribble a small amount of water into your bilge. Rebedding them at some point wouldn't be a bad idea, but you will need to remove the anchor locker pan to get at the nuts underneath the forward pulpit legs.)
Your other stanchions should at some point be rebedded as well, which is just normal maintenance on an old boat. Note, by the way, that in the E26, there is a headliner covering the nuts on both of those bow pulpit legs. I went ahead and cut two holes in the liner so I could access those nuts. You could make a vinyl cover for those holes if it bothers you. However, in practical life, that is so far forward in the vee berth that you can't even see it unless you are up forward with your head stuffed up in the forepeak and are looking for it--something I never do anyway.
As for the fuel tank: You can absolutely replace it with the boat in the water. I've never tried removing it, so I can't say whether you could accomplish this with the engine in place. If your boat is like mine, you have a wooden shelf over the top of it that you'll have to remove in any case. I'm not sure whether you would have enough room to move it over the engine. However, even if you had to remove the engine to get out the tank, that is not a terrible job. (I've done it.) With the engine removed, yanking the fuel tank would be very easy. Again, people here could talk you through removing the engine. It's not as bad as it sounds--especially for an engine as small as the 1GM.
Replacing the exhaust and raw water hoses should not be a big job. Concerning the exhaust hose, which attaches to the transom, I presume you have a removable access panel in the quarter berth that will allow you to crawl in underneath the cockpit. If not, you should cut out the panel and fabricate a removable one. (Mine wasn't originally removable, but a little bit of work with a saw took care of that. Other E26s I've seen already have the panel removable.) Bear in mind that if you decided to pull the engine to remove the fuel tank, you could very easily tend to the exhaust hose at the same time. You'd have clear and clean access to everything that way. And, if you are really ambitious, you could take your engine home and give it a spiffy paint job!
The 1GM is a good little work horse of an engine. Once you get it up to snuff it should give you years of solid service.
I hope these initial observations might prove helpful to you and not make you feel overwhelmed. It may be that some of what I'm presenting here is a "full monty" approach, such as taking the engine home and painting it. I'm not sure you even have to remove the engine to get out the fuel tank; I don't know. But I guess that what I'm saying is that even if you have to--and it does sometimes happen that projects like removing a fuel tank can have a cascading effect--don't lose heart! This is all doable.