[Closed] advice on chain devices etc please

i have an old heckler that i only really ride in the alps (uplifts, little or no uphill riding) and the odd uplift at inners etc

its already pretty beefy with lyrik forks, deemax wheels, 2.5 d/h tyres etc.

it currently has 3 chainrings which are not needed so;

1. If i fit a bash what size do i need? Do i get one the same size as the ring that has been removed or do i get one the same size as the ring it is next too?

2. Do you only have a chain device if you run a single setup?

3. If i go single ring setup what size front ring and rear cassette would people recommend?

4. anything else i need to know and/or consider?

thanks