If you're installing on a fresh 3.55 OFW console, install the Rebug REX firmware first of all, and if you ever want to convert to DEX (debug) firmware, then use Rebug Toolbox to dump your eid_root_key and use the CEX -> DEX conversion tool.
If you do happen to go ahead and do that, and a Rebug update is released in the future, grab the D-REX firmware PUP from the site instead of the normal REX PUP.
(tl;dr, CEX -> Rebug REX firmware; DEX -> Rebug D-REX firmware)
Be aware you cannot go online or use PSN features on a DEX console/firmware. See below answer.
Regarding installing a different firmware, you aren't stuck with it at all; you can still go ahead and install the other desired firmware if you so wish.