A fan and a dehumidifier would be my first purchase. The humidity in the air isn't going to help very much and may make thing worse if you leave the cellar door open.

Dripping wet fiberglass is a perfect breeding ground for mould. Get rid of it. And the last thing you want in a damp basement is more humid air.

Get a dehu going there immediately. Run it all the time you are there on the weekend. Empty it just before you leave so it runs (and shuts it self off when reservoir is full) after you leave.

As for opening the cellar door, if you do that you will see an immediate rise in condensation when the warm moist outdoor air hits the stone walls of the basement. I might do that while I was away from the house buying a dehu, today since you may have such an accumulation of moisture there by now and could lose some in the ensuing air exchange. Obviously, you don't run the dehu with the door open. And the cellar door should be closed at night when dew falls (which would add humidity to the basement). Plus animals may come if it's open at night.

One of the problems is that you can't run a dehu (unless you get a complicated, somewhat pricey model that pumps the condensate upstairs to a drain) when you are not there to dump the reservoir a couple of times per day. Do you have a local contact or watchman that could do that for you over the next few weeks?

I would hold off on removing the insulation until after you've had a chance to dry out the area. It may not need to be replaced.

Don't pull up the plastic on the floor. It's there to impede rising moisture vapor fom the soil ( ayear-round as opposed to seasonal problem). There are better solutions, but it will be fine, for now.

You can buy dehus at any big box hardware home center. Get one with the biggest reservoir, for your convenience.

You may be able to rig up some Rube Goldberg arrangement to deal with the condensate when you are not there, but a simple portable model will work immediately and you'll be surprised at how much effect they have in first day.

They are not cheap to run, however, so expect your power bill to rise.

Be comforted by this fact: the problem is at its worst right now; even if you did nothing it will seem better in a few months because of the changing seasons. Unfortunately it won't go away, just temporaily abate.

So get that dehu and get it cranking - that will start the process of reversing what's going on so you can accurately assess what needs to be done in the long term.

Oh, and congratulations on buying an old cottage. It sounds intriguing.

L

Even if the sagging dripping wet fg were magically rendered dry as a bone, the ceiling of a basement is not where insulation belongs. See link.

Most portable dehumidifiers have a provision for continuous drainage. Connect it to a floor drain, or even a flex hose through a small hole to the exterior of the basement.

Here is a link that might be useful: Basement Insulation Systems

Worthy, the OP wrote that there was not a floor drain.

As for draining through a small hole to the exterior of the basement, how does that work? Are you suggesting drilling a hole through the wall and somehow draining into the soil at 8 feet below the surface? Or do you mean pump it up and out? Do they make portable humidifiers that will do that sort of pumping action?

There are dehumidifiers with up to 16 feet of vertical lift. See link. (Not a personal recommendation.)

Or you can put the dehumidifier on a bracket or stand; many basements, even with eight foot or higher ceilings, are actually only four feet into the ground.

Woops, lost the link. Dehumidifiers with condensate pumps.