If, for example, you want to be able to just put a book, or chair or whatever, then there is no need to make them into proper sprite tilesheets.
To understand what I'm suggesting, have a look at the tile sheet !Other3. You will find it under Graphics/Characters. You will see 2 sorts of objects there. Some of them, e.g. top left, have 3 versions of the item. That is because they are animated, like the candle, or the water around the rock. To use those, you put them into a graphics event set to stepping animation. Others, e.g the pickax, have only one version of the item. That is because you don't need these animated, you just need to be able to put them on the map. These you place with a graphics event set to Direction Fix.
All you need to do is to create your own sheet like that. You can put animated objects on, as long as you only want them to do something like the candle, or the fire, smoke etc. from !Flame. But mainly you would use this for single items. !Other3 is 384 x 512, so to be on the safe side, you could make your sheet the same size.