Any medium to light reel will do. DON'T overline the Launch.

It is MADE to cast a 5wt so use a 5wt. The Launch loads pretty quickly. Use a WF line if you're not casting too far most of the time.

IMHO, putting a heavier line on a rod is done too often 'cause anglers aren't using the right rod for the situation. Since you already have a nice 4wt, the 5wt will find it's right place.

Have fun, ... Oh, .. there is no cure!!