1) I suppose your question on how to measure light with a TTL meter aims at measuring incident light rather than reflected light. (Reflected light is easy: Aim and read.) You can sort of measure incident light by placing a Kodak Gray Card at the position of your subject and measure that Gray Card. Make sure that it fills your viewfinder completely.(posted 9099 days ago)2) The type of meter you buy depends on what you want to do. For detailed measuring, a spot meter is a great thing, but you must acquire some theoretical background, or you will be badly disappointed. Also, spot meters are not usually very sensitive, i.e. if you measure in dark rooms (churches and the like) often, the spot meter will not indicate anything. For such purposes, you need a sensitive meter, such as one of the high-performance Gossen models. If you want to measure flash, too, make sure, the meter you select has this feature.
3) If your hand-made developer is fine, stick with it.