Using ESPP stocks to pay for my house down payment

I am sale agreed on a house and besides my mortgage and money easily accessible from a saving account, I need about 25,000 euros, including stamp duty, solicitor fees, etc. I have a bit over 35,000 euros worth of stocks I acquired through my ESPP company scheme and some additional money locked in a few saving accounts I’d rather not unlock straight away (but I will if needed).

I am just not sure how to assess how much money I will really get out of my stock, after being taxed on benefit, the exchange rate for dollars (it’s an American company so stocks in dollar), and the fluctuation of the stocks. I also have no idea how to decide when it’s best to sell it, and how much I should take from my stocks rather than my other savings to pay the least money.

I know about the exemption on a certain level of benefits per year, but my colleagues also told me you get a better tax situation of you resell your ESPP within one month of acquiring them, but I can’t figure out of they mean the standard exemption for stocks or something specific to ESPP.

Anyway, I can tell I am quite novice with that, so I am not sure if that’s something you can figure out on your own by reading the right links or it would be best I pay someone to help and if I should, then what kind of specialist? I worked with a tax advisor in the past when I was Form 11 and was really satisfied, but I’m not sure if this is just about tax?

Would you have any suggestions to help me understand how I could figure that out? Note that I am not trying to save a few hundreds (if it’s just about a few hundreds that’s fine) but I am not sure whether I can lose a few thousands that would make a difference with the down payment if I sell my stocks without thinking much about it.