I'm actually ok with a large stable, assuming those on the bench get some portion of experience as well. If not, nope!
There's no experience in this game. There's permanent upgrades and unlocks between runs of whatever characters one enjoys playing with, and some temporary upgrades.
The game goes like this:
1. Start a run, chose which four characters to use.
2. Drive the coach to the Altar of Hope (permanent upgrade mechanic).
3. Short run with some very basic encounters to the first Inn.
4. At the inn, chose some temporary upgrades, choose the next destination, rest and get relationship changes.
5. Do the destination, reach the next inn.
6. Same as 4.
7. Do this loop a maximum of four times or until one beats a boss which allows one to attack the Mountain where one of several final bosses can be fought against.
8. After either retiring (at an Inn) or a wipe, start over with upgrade currency to spend at the Altar of Hope (step 2). A wipe leads to a loss of a lot of the upgrade currency.
During a run one has only four characters, which can get skill upgrades for this run. But if one dies it gets replaced by a random unlocked character at the Inn, so in this case one can get a suboptimal character which sort of sucks.
The upgrade currency (candles of hope) gets decreased a lot if one has a complete wipe, and continuing a run with a non upgraded character increases this risk. So thus far, I've always chosen to quit the run at the Inn if I've lost a char, to be sure I get to keep all the upgrade currency to increase the chances next run instead.