I doubt there is a FI "kit" for the VTX1300. It would be a HUGE undertaking requiring a new computer, removal of the carb, replacement of the throttle body, wire harness, air intake, etc. By the time you finished you would have many thousands into the bike. If FI is that important to you, buy a VTX1800 or a VT1300 (all three models of which - Stateline, Interstate, and Fury - are FI).
For seats, the two most common recommendations are the Mustang or the Ultimate. Both are expensive and can sometimes be found used. The Ultimate and possibly the Mustang have various models that depend on your body type (height, girth, etc.).
My opinion only - the best bags for a VTX 1300 are the Tsukayu VTX specific. Large, good looking, sturdy, and require no electrical/light changes. However, they come unpainted so you will have to paint them. Lot of other choices. Research carefully any that you consider. There are at least two that have had manufacturer supply problems (e.g. taking money and never sending bags).