Where can I see how much ETH are exchanged at any given moment ?
I only see the marketcap / volume (24h) / circulating supply.
What can I understand with this information ?
This
https://cryptowat.ch/Click on the Exchange name for more data
Just a personnal opinion, injecting the majority of your initial investment with ETH,is how to say... really crazy. ETH is mainly based on the buzz around it. Are you from France? With such a big amount, your bank account will be flagged direct!

More than 10 000 in a month don't forget Tracfin will list you on his list for review

Good luck with what you decide