possibly re-locating to Algarve in new year

Welcome to the Forum 

I can't exactly help you with your questions as such, due to Brexit just around the corner. I can direct you to British in Europe where they can give answers in relation to Brexit.

SimCityAT
Expat Team

its a starting point, thanks much appreciated

I can't give any advice whatsoever re employment  ~ other than to say if you would need an employment income to survive then don't even think about moving / giving up your present job  until you have that sorted.

Outside of tourism / hospitality I can't think of any area where you would not need fluent Portuguese.

Apart from that though : if your main issue is that every three months you would have to attend at a hospital / clinic for medical procedures, then I would say that that alone need not motivate a choice of location.

The whole of the Algarve is served by the Linha do Algarve trainline , and nowhere is much more than an hour from the central and main station of Faro.

Unless you particularly wish to live close by your daughter / son in law then I would think that the whole of the Algarve is open to you : so rent somewhere for three months and use the time to explore till you find somewhere which suits ( which from what you say may well not be a seaside resort ).

If you  wanted someone ( it would not be me ) to give more specific advice as to employment opps then you would need to provide detail of your area/s of expertise, level of Portuguese knowledge, and  daily rate / monthly salary desired and so on.
Maybe these would lend themselves to self employment  ?