Welcome, my name is XXXXX XXXXX X will do my best to help with your issueHook up your electric in parallel, there is nothing to be gained by piping it in series. In fact it's less efficient since you will have standby loss in series with the second tank.As long as there are to stops between the new tank and the expansion tank you don't need to do anything in that regard. What you have now will work fine with the new tank. Pressure tends to equalize throughout the piping systemSince PEX is standard size you can probably use your crimped connections and fittings on the Wirsbo. I've used Watts crimp rings on many different brands of PEX but never Wirsbo. That said push lock fittings are a sure thing.