I'm curious if @itmeJP and @DansGaming have had enough experience at lvl 4-5 (either with their own character or as a group in general) to alter their decision of what might be a better composition for the core group compared to if they were lower levels. Even at level 3 you can pretty much pick whatever and not worry too much about contributing because attack and spell DCs are pretty low, your tool kit isn't super extensive/diverse , etc.
I think it's pretty safe to say that someone is going to go the arcane magic route. My own personal bias says "Wild Magic Sorcerer" for RNG hijinks and personal experience (convincing a Unicorn you randomly summon to help you fight is interesting) and metamagic (Twin Spell). Plenty of Wizard options to fill out whatever kind of area you want to specialize in (Blasting/Battlefield Control/Summoning/etc). I will say an option disappointingly not available, that would be interesting fluff fitting into the setting would a Bladesinger from Sword Coast Adventurer's Guide to intertwine with a elves/notelves storyline.
Hell if I know what else would fit... I will say though that while the group + guest tends to do pretty well with whatever they pick, I'm thinking maybe another class that isn't super reliant on any one resource; Fighter, Ranger, Rogue, Monk... Paladin is probably the line of "I've run out of shit, but I can still lead us to safety until we can get our resources back". Again, never been a "You always need a healer" kind of guy but to each their own - someone with the healer feat wouldn't go amiss.