Hi Blake,

If your hot water tank is not corroded and in good shape, try checking or replacing the pressure release valve. I purchased one from Defender Marine supply for about $50 and it resolved the issue for me.

Blake, welcome to Catalina club. 
these are all common wear and are easily fixed.
I would suggest not taking it out of the slip until you have fixed in this order:
1- replace collapsed fuel hose. Easily done. 
2- you have not indicated what is leaking from the water heater, antifreeze or water.  If antifreeze,  try tightening the hose clamps first. The same if water is leaking.
The water heater is easily replaced if all fails. You can find plenty of info here when you search for it, you can also look at the website listed on my signature. I replaced mine recently.
3- chain plates are easily fixed by digging out the old caulking and clean the area and overfill the gap with 4200 3M caulking and install plates.
All else can wait until you have completed the above regular maintenance. Fortunately you can do all of your list in you slip.
Have fun, post photos of your projects here to help someone else.

Blake, 

I recently purchased 832 - 5 before yours. :)

Cheers!
-gerald

Regarding your CNG stove, I would suggest contacting a company like Airgas for the correct hose coupling to the tank. They may also be a resource for tank inspection (there are laws governing the acceptable tank age for refills) and I think they might also be able to help with methane refills. 

This hits close to home. 5 years ago I bought my first Catalina 36 1984 (I still have it).  I'll tackle the major issues; the rest seem like routine upkeep. My plan was at the time and still is island-hopping (cape and islands,NY) until I upgrade to a Catalina 400 or 42 for the Bahamas. So far so good, my wife and I love 3-5 day island trips and a yearly 10-15 day adventure. I decided to invest heavily up front to ensure minimal system failures.  Notice I did not say "avoid system failures".

1. You should simply replace the water heater which means potential fuel tank removal an opportunity clean inside of the fuel tank and change fuel hoses.
2. CNG vs. propane: researched CNG extensively (CNG is better), but availability in the States is limited. I recommend swapping to propane which means changing orifices/connectors, setting up a propane closet in the lazarette. I opted for a new propane stove from West Marine, including hose replacements, solenoid, and cabin switch. It's an investment, but cheaper than salvaging a burnt boat.

The 25 Universal engine, at 40 years old, had a cracked hot water housing (part of the block). For reliability, I got a new engine, costing around 10K. This required replacing the entire exhaust system, and switching the shaft brass to stainless steel, along with a new prop.

There are other purchases but I can't risk discussing here, in case my wife sees this forum.

My 1984 Catalina 36 Mk1 has a hot water tank leak as well.  It's leaking from the bottom of the tank so it must be rusted out.  I bypassed the tank and just get by without hot water for now but would like to replace eventually.  It looks like the only way to get the tank out would be to either remove the fuel tank (and possibly the refrigerator compressor) or to remove the gally counter top and pull it from the top.   I've been wanting to replace the counter tops with a more modern style so I make take this route.
The CNG oven/stove was toast and replacing with an equivalent propane system is very expensive.  Reviews on new propane stoves seem to indicate that these expensive stoves are unreliable and fail within a few years and have little to no customer support.  I decided to just replace with an electric convection oven and electric cook-top and built a cabinet in the space to hold them.  I had enough room under the oven to add a cabinet for holding pots and pans.  I have a propane grill in the cockpit if I need to cook something while away from shore power and if I really want to use the electric oven/stove without shore power I have a small Honda 2200 generator that can power the boat.

First, the hot water heater.  I have 1985 MK I boat (hull 495).  I replaced the hot water heater by removing the cabinet under the sink.  You remove the entire thing, drawer, flip out tray and the frame.  Once the frame in out the hot water heater is accessible.  Buy the replacement from Catalina Direct for a best fit.  Note:  The mounting may be rotted or just a little short as the new mounts seemed to be slightly longer.  One thing I did was to cover the top of cabinet frame with a piece of starboard.  That kept condensation out of the drawer and flip out tray.  Another thing I did was cut a large opening in the outboard side of the cabinet.  That allows access to the hot water heater for inspection and possible future horse replacement.

Second, I'm a proponent of CNG.  If you live where it is available, make or by fill pump adapter.  The cost of CNG is very inexpensive (last year I spent $4.69 to fill both tanks).  I have two tanks, as we are out for much of the summer.  My Magma Catalina grill is also pumped to the CNG tanks.  I can furnish details, anyone is interested.  I my stove craps out, I'll by another CNG stove, rather than covert to propane.  The hose must be for CNG, not the hose used for propane.  It 3/8" I.D. with a 5/8" O.D.  Between the regulated pressure near the tank, it is advisable to quarter turn shut off valve, made for CNG.  It is a safety device to protect against leakage into the boat when the tank is shut off, in case of a leak of the tank valve.  Sorry, I don't have the thread size.  

Blake, maybe not the best picture of me or the grill.  Notice the yellow hose going to the grill, it is a flrxible metal hose for natural gas, the end fittings are attached to the hose it self.

Blake,

While Lake Erie looks close on a map, the round trip to it from our marina in Lake Michigan is about 1,200 nm.  I know I made that trip some years ago.  We were only on the Western end of the lake, but we logged a total 1,325 nm. and nine weeks.  Of course, that's what boats are all about.