Will my portal have hotels in small towns, or only in the big cities?

Yes, small towns do come up, but the choice there is usually much thinner than in a big city. A hotel booking API does not hold any hotels of its own. It passes your search on to suppliers who have signed agreements with properties, so your portal can only show what those suppliers have on their books for that place.

In a large city or a well known tourist spot you will normally see hundreds of properties, with several room types and rates for each one. In a small town you may see ten or twenty, and often those are the ones that already sell online through the bigger travel sites. Family run guest houses, small lodges and homestays that only take bookings by phone are usually missing, because no supplier has ever signed them up.

If your customers ask for one region a lot and it looks empty, the usual answer is to connect a second hotel supplier alongside the first. Suppliers are strong in different parts of the world, and one may cover an area well where another has almost nothing. Whether you can add one depends on your plan and on that supplier agreeing to work with you, so it is not something anyone can promise in advance.

Before you decide, write down the twenty or thirty towns your customers really book most often and search each of them on a test portal. That gives you an honest picture of the coverage for your own business, instead of a general answer.