I would recommend starting with the complete Legacy package with the ZW transformer for power with all interconnecting cables. That will allow you to run all the new and old conventional trains with one controller. Accessory controllers will need to be purchased if you wish to control your accessories via remote.
http://www.electricrr.com/AcDcCommander.htm. has an upgrade board for older conventional locos if you wish to upgrade them to command control.
Larry