I bought a forgotten cellar near Paris with 500+ bottles, including Dom Pérignon 1976 and 1970s Burgundy. Help!

I’m about to take possession of an underground (-1) cellar near Paris that contains what looks like an entire amateur wine collection(~600 bottles) and I’d love some advice on what to do next.

The backstory is a bit strange. A company owned several cellars in our building but seems to have forgotten about them for decades. They weren’t properly secured, so residents informally started using them. During recent building renovation works, the company began receiving bills for the cellars, realised it still owned them, changed the locks and started selling them off.

This one remained unsold until I bought it. The wine was presumably left by a former resident, but there is no paperwork showing who the bottles belonged to or when they were bought. I have a suspicion it was one of our older neighbours who passed away a couple of years ago but can’t be sure.

What I can personally confirm is that the cellar has been untouched for at least eight years. I own the cellar directly next door, use it regularly, and have never seen anyone access this one.

From what I’ve seen so far, the previous owner was clearly a passionate amateur collector rather than someone buying bottles randomly. There are often multiple bottles from the same producer, domaine or vintage, sometimes 20 or more, as well as lots of older labels from small or now-obscure producers.

Some of the more interesting finds so far include:

Six bottles of Dom Pérignon 1976 in a sealed original case

Several bottles of Richebourg from 1972 and 1974

Multiple older Vosne-Romanée bottles

Château Chauvin Saint-Émilion Grand Cru 1978

Various Burgundy, Bordeaux and Sauternes from the 1970s onwards

Multiple magnums

Several unopened wooden cases

Photos here : https://imgur.com/a/TzbCnos

I’ve moved the bottles that appear potentially most valuable, mainly the Champagne and Burgundy, onto racks in my own cellar next door. There are still at least 500 more bottles of mostly wine (some spirits) to inspect.

The condition is mixed but probably better overall than the photos might initially suggest. Some bottles near the front are heavily mouldy, and a smaller number show serious seepage or failed corks.

However, around 90% are simply extremely dusty, have mould bloom on the labels or capsules, or have labels stained by another bottle leaking above them. Most fills appear to be neck or high shoulder, and the bottles further back generally look much better.
I’d like to clear the cellar reasonably soon because we want to start using it, but I also don’t want to move, clean or dispose of anything in a way that destroys value or useful evidence of storage.

My main questions are:
How would you triage and document a collection of this size without unnecessarily handling every bottle?

Does eight years of personally observed, untouched underground storage help at all when the earlier provenance is unknown?

Who would you contact in France for an in-person assessment: iDealwine, another auction house, a specialist merchant or an independent expert?
I’m not asking for individual bottle valuations or trying to sell anything through Reddit. And how long do you think this is going to take?

I’m mainly looking for advice on triage, provenance and the right type of professional to approach and establishing whether this is going to be worth the hassle.

Thanks in advance for any help!