intrisicly safe.
To make the sensors explosion proof in a methane fume environment for the specific parts you listed is not possible.
it is like asking if you can make a pack of matches intrinsically safe.
the explosion proof enclosure with window can be had, but often needs a few weeks to get on order.
as a note, all the threaded wire ports have to have 5 full thread engaged, and the backfilled conduit lines have to be done to the correct requirements.
as for anyone offering your offer, I highly suggest that if you do not understand the liability for intrinsically safe, that you make that exclusion in writing.
not sure if you can run a bluetooth through a 1 inch thick aluminum walled enclosure. that part might be a bit tricky as well.
EVERY part that is exposed to the explosive atmosphere has to have so little current that wires that are shorted will not have enough energy to make a spark. that eliminates almost everything we do.
as for the rest, that seems simple enough.