Years ago I created a spreadsheet to find the monthly cash / net cost of major assets I was considering: houses, cabins, boats, cars. You would be surprised at the cost when EVERYTHING is taken into consideration.
I have no idea where Tulda is and whether your state has sales tax, but Washington State does and it's roughly 10%. And most vessels are sold through brokers, so there's another 10% (or you have to learn essentially a new trade to get it sold yourself).
So for "a few years", that's -20% right out of the gate.
Depreciation...we'd all love to have a crystal ball there. Is China going in the toilet? Some models are predicting 0% growth there and lots of pain. And China is Washington State's largest export customer. And lots of the boats talked about on this forum are in Washington State. And is the trawler market growing or shrinking? There was a monster thread on just that topic (no obvious conclusion).
The working on it yourself that RTF mentioned - that's getting harder too. Lots of marinas discourage work that makes noise and dust. But if you're in a major boating area you can probably get that handled at a predictable cost.
KK's are not without issues, a couple of which are coming up on 25 years of age on the type of boat under consideration. Early (many? most? not sure) KK's have end-grain balsa coring in deck and superstructure and water intrusion has lead to issues. More problematic, KK hulls into the mid 80's were fully foam cored (they switched to solid fiberglass below the waterling) and failures there have lead to hull strength problems. And then there are hull blisters.
And fuel tanks. KK epoxy coated their tanks so they have fared a lot better than (for instance) Grand Banks tanks, but...we are really approaching a time when some of these 25 year old boats may face some emerging issues.
There's a rule of thumb (happily debated, of course) that a boat generally requires about 10% of its original purchase price to "keep up" each year. Moorage, insurance, and licenses are included - but fuel, liquor, transient moorage, and restaurant bills are not.