Jakob, I'll try to answer some of your questions quickly, but you can email me privately any time you need help or advice with the boat. I've been through this boat from one end to the other!
My decks look good, but have had 3 leaks that I know of since I've had the boat. Removing them is on my short list. Sure dread it!
Fuel tanks look good, but I've known several Albin 43's that had to be replaced. Got my fingers crossed. Removing the teak decks will go a long way toward protecting the tanks.
Windows are pretty good. Have had to clean tracks on movable ones, and reseal the front fixed ones, and all port holes need new gaskets. On my list.
Most of the panneling is good, except below leaking port holes. Some damage there, but mostly cosmetic, nothing very bad.
I installed a new 50 gallon waste holding tank a couple of years ago. It's under my galley floor/ forward part of engine room below my genset. I also replaced ALL sewage lines, macerator pump, and both toilets. I put VacuFlush in mine and love them.* Ronco is the place to get the tank. They are "semi-custom" and will put inlets / outlets anywhere you want them.
Other projects I've done: Large house battery bank (8 golf cart batteries). 2500 watt inverter / charger. 3 Reverse cycle air conditioners, 2 16's and a 12. Oil changer system that drains both engines, transmissions, and genset. Washer/dryer. Wetbar on sundeck with icemaker. All new electronics, (radar, chartplotter, 3 vhf's, 3 gps's, 3 depthsounders, stereo system, Surrond sound in salon, built in computer with monitors in salon and flybridge, etc). New custom salon furniture. (including a pic of computer desk in salon) 120 amp alternator with smart regulator on one engine, and in process of adding a second on other engine.
There are other countless projects I can tell about, but this should give you plenty to think about!
Keep us posted on your progress. I'd really like to hear about the teak deck project as it progresses.