First I recommend posting in the Rules section

Second: Welcom to the forum

And now your questions: you can connect both Dominix with the coupler since the sabers and the coupler are MHS (Modular Hilt System) compatible. You don't have to order another pommel except for a new look of your saber. You simply unscrew the pommels that come with your sabers, screw the coupler into one saber and screw the second saber onto the coupler.
The blades on all sabers (except the Initiate sabers which come with a 24" blade) is a standard 36" long blade, but you can always request a shorter one (for example 32") in the Order Comments.