The express install is sufficient for almost all players. We recommend only installing extra mods if you've played with the defaults and specifically find them lacking. For now, ASSUME ALL MODS NOT EXPLICITLY MARKED AS COMPATIBLE WITH RSS/RO/RP-1 WILL BE INCOMPATIBLE!
While you're installing really important stuff (RSS/RO/RP-1) CKAN will suggest extra "recommended" and "suggested" mods for you to install along with them. Do NOT let it install those mods yet! Instead, write down which ones look interesting, we'll come back to them later. Again, DO...