I’m thinking about acquiring Swamps.....will be playing solo ...do y’all recommend combining the cards for each into one huge deck...or is that overkill?
Everything's designed to be combined except the Loot and Scavenge decks, and the Exploration counters. Combining those can throw off the odds. In particular, the Exploration tokens can make it harder to find clues when you need them.
Some people also suggest things like, "Only include one set of passages" or house rule "if you draw two passages in a row, re-draw the second one" or otherwise fiddle with the map deck. That's optional.
Otherwise, yes, mix everything together.