I just got my 50th S rank at 475 hours(playing the international version) and the rest of the trophies are not far off. I'll also echo sentiments that it is very much possible solo. My gear ended up being;
Ox Tounge+5(no element)
Ox Tounge+4(Earth)
Flame Spear+8(Fire)
Flame Spear+9(Water)
Emeral Spear+10(Wind)
Dragonscale Shield+9
Wyvern Plate+7
Fire-dragon Cuffs+6
General Pants+10
General Boots+10
I also had Fire-Dragon Boots and Fire-Dragon Pants for enemries that use magic(both at +5) like elementals and Primeval Guardians. Aiming for this gear on a spear setup will help cut down on time tbh.