PoA has to be the first thing to get moving asap - health/welfare and financial
Get him to help you do a list of all the bank accounts, insurance, isas, suppliers etc. If a family member can get added to things it makes it much easier to help deal with them
If he's been doing online banking, get it transferred to a non internet account (caused no end of trouble for my parents)
If he's willing, set up a new bank account for him and set up a direct debit from the main account to put an amount of money into that a month for spends and take the bank card, cheque book away and store safely for the main one (and any other accounts). Then he can get money out, be independent, but the damage that can be done by scammers etc is really limited.
Support him to go to any groups that he might possible enjoy - dementia can be incredibly lonely, and now is the time he might cope with the new environment.
Talk to anyone who might have personal experience in local care, facilities, or services - word of mouth is an amazing thing. My parents have an independent carer who is so flexible and properly caring, but never needs to advertise as she is always full just by word of mouth
Things might go quickly, or slowly - no one can predict this, so you do need to keep an eye on things. And it can be very hard in the family for people to accept things sometimes, so you do need to talk about the future. Anyone who says 'he's never going into a home' is unrealistic, but theres lots of stages between now and then.