Can it be used indoors

Yes, the folding stove can be used indoors, but make sure that the fuel source is also safe for indoors use. The shelf on which the fuel sits is elevated about 1/2 inch from the ground, which prevents the surface underneath from being scorched. Nonetheless, I put the stove on a cutting board, just to be safe. I tried out the stove in my kitchen to prepare a few meals. The surface under the stove was not scorched; my smaller regular kitchen pots worked fine on it; and the stove cools down within a few minutes after the flame is extinguished. Of the various fuel types that I experimented with, the alcohol burner seemed to be the cheapest and most reliable. I hope this helps. ~Robin

What type fuel(s) is best to use with this indoors?

I like the Esbit alcohol burner for indoor use. That type of burner uses denatured alcohol which is relatively inexpensive and easy to find. 3 ounces of denatured alcohol will give approximately 30 minutes of burn time. You can find it at Home Depot, Walmart, paint stores, and other retailers that sell home improvement or painting supplies.

Does this stove produce enough heat to make a pot of coffee in a standard aluminum percolator pot? (Smallish pot, 6-cup or 9-cup)

It would but 2 cups, 16 oz takes around 12.5 min. Adjust distance of can to pot to 1 3/8". It makes a difference.6-9 cups would take a while. Coleman propane stove is better for a big pot of coffee.Sterno's main advantage is for cooking indoors. Safer.

What fuel is best for boiling water?

Assuming you are an outdoor interested type. Mineral spirts - Denatured Alcohol. And use proper burner for a clear blue flame. Liberty Mountain by Westwind is a very good setup and is both quenchable and pocketable. Useable at most all elevations. There are others! Must carry a fuel bottle as supply source of the expendable fuel and a lighter. Spill WARNING does apply!! Requested Additional information to comment: The unit can be purchased as an assembly or as components,(stand or burner). The burner is a Trangia assembly by brand lable. Used on Europe for years. I have used it extensively. It burns cleanly and leaves no trace of its presence and is quite safe. It is not a warmer for food! It burns way too hot. Makes quick Tea or Coffee from boiling H2o and cooks well if you give it attention and stir; or burns rapidly if not. It helps to raise the heated container another 1.5 inches if the desire is slower. A military canteen cup stove is just about correct. The cup performs outstanding also. It is a balancing act when using a large container on a small surface. CAREFUL! Enjoy!