Do you have access to sunlight? A solar panel can be installed to keep things going with the battery connected.

Order of cable removal does not matter, however, convention states to remove the ground wire first. This is to prevent sparks should the wrench slip and contact ground.

RE: If the wrench is on the ground terminal and it contacts body metal, no spark.

If the wrench is on the power terminal and it contacts body metal , spark.

Note, older cars from the 1950's had positive ground so I've referenced ground as the wire that leads from the battery to body / frame / engine block.