1) Replace Spreader Brackets
2) Step the Mast and hook up wiring (while the mast is down - any electronics I should add? New VHF arial maybe? GPS antenna (or is it better to mout GPS low in the boat?), maybe Radar?
3) The icebox and sink drain do not have a seacock on the outlet, but a regular water valve (gate valve I think) - should I change this? Is it urgent?
4) The diesel fuel tank is loose - the fiberglass matting that holds it in place is loose, and the tank is essentially loose to slide around. Any advice on this?
5) The bow pulpit is bent - should I try to unbend it, or do I need to buy a new one?
I paid just $2,000 for her - just need to haul her to water (20 miles) and step the mast.
I'm going to assume that you're working on a pretty tight budget, so you need to prioritise. The three things you need to worry about, in order of importance are:
Make it float
Make it go
Make it comfortable
You mention that the diesel tank is flopping around, and that the fibreglass has become loose. Based on this, you should assume that there are some issues with the hull that need to be taken care of...
Is the boat in the water ? If so, start by taking out everything that you possibly can, and then drying out the bilges completely. Now start looking for water. Leave the boat in the water for at least 48 hours. If there is water coming in anywhere, figure out what is allowing it to come in and fix it. Don't ignore a slow leak thinking that the bilge pump will take care of it.
If the boat is not in the water, then put it in and do this before you spend any money elsewhere. You don't want to go out and buy new spreaders or pulpits, only to find that you can't afford to replace the shaft or the seacocks.
Next, while the boat is in the water, get inside and close it up. Now get someone to spray water on it everywhere. Look for leaks, particularly at the stanchion, ports, hatches, and deck hardware. If you find any - fix them.
Now, before you put your mast up, assemble everything to make sure that it all goes together as it should, that all of the pieces are in good condition (no cracks in the metal, no burrs on the shrouds and stays. Don't try to use rigging that is in poor condition. You, or someone else can get killed very easily if the rig comes down or pieces come loose and start flying around.
Buy new lines for all of your running rigging. Use something like 3m silicon spray on all of your sheaves and blocks and make sure that they are running smoothly, and that no pins are coming loose anywhere. This is the time to put on new spreaders.
Now check out your sails. Examine them carefully for signs of wear, fraying, and loose stitching. If there is loose stitching, get it fixed. If you don't, the sails will probably tear at some point, leaving you with a much bigger repair bill.
The next step is to make sure that your engine is working. Check your oil levels, thermostat, impeller, all hoses, battery connections, stuffing box, anything and everything you can think of, and can find in the owner's manual (which you should be able to download if you don't have one).
So at this point, you have a boat that floats and that can go. If you don't have the wherewithal to replace the bent stainless, then take it off and throw it away if you can't bend it back into a workable shape. Your boat will sail fine without them and while they do add a margin of safety, there are thousands of boats out there that have never had them. I checked out a couple of pics of the Cat 27 - it doesn't appear that it has an actual bowsprit - so I am going to assume that you are referring to the pulpit (the steel frame on the front of the boat).
If you have any money left, then you can start replacing/repairing/upgrading the interior.
Good Luck !