Afaik there will be some problems though. First of all you would use view aligned billboards and fake an isometric camera (like in isotest). Then when you load the billboards texture, you must match the ratio of the billboard to the loaded texture. Probably you will want to use a custom uvanim shader so that you can use a sprite sheet- this modifies the uv coordinates across an image so that you only display a subset of the image.
Sprite rpgs are the coolest
but drawing sprites is very hard... Good luck.