well you already know that a tub has an overflow, so you are far ahead of many wannabe DIY.
The overflow you buy at a store. Look at the Geberit web site or others to get an idea of options if you want to feel comfortable with it before you start, but it is not a challenge so you can safely skip this until you need it.
Once you have an idea of the tub you want to get, look at its PDF file on the manufacturer's web site to see where the inches go, for the drain (and overflow). From there you calculate the route your new tub P trap and drain pipe will take. Then you buy the parts as need be.
Water supply (hot and cold), mixing valves and spouts are not hard to figure out either. Many threads here have dealt with little problems with old spouts. (Search and you will find.)
Plan your layout, and post a diagram here, so people can comment on what needs to be done.