I happen to work at a place with 4 inns reachable from a single location, and 2 others within a 50 foot walk of that, but even then, when you're often only getting 2 energy per check-in, it would take forever to refill.
The bigger problem is going to be the cost of increasing vault capacity. A single potion vault space increase (which gives 10 extra slots), costs 200 coins, which is roughly $2-$3, depending on how much gold you're willing to buy. I only played for maybe 20 minutes, and my inventories are already nearly full. Since crafting potions work on a cooldown system, you end up wasting a lot of time waiting for potions to finish (and a lot of inventory space and pickups waiting for the right ingredients to actually make stuff. For having over 150 ingredient items, I find it odd that after making the tutorial potion, I still don't have enough of the right kinds to make even a single potion!)
Ingress had a pretty decent monetization scheme, and Pokemon Go was slightly worse (but not too terrible as long as you had access to enough Pokestops). This game is going to be practically unplayable without both access to a large number of inns and a willingness to spend a lot of cash.