Almost everything is possible Solo, you can still Level with Tier 1, Tier 2 and Tier 3 Powerful Gear Only Pinnacle Activitys require a Team (Trials of Osiris, Raids, Dungeons, 100k Nightfall, Higher Tiers of Nighfall The Ordeal and Higher Tiers of Nightmare Hunts and Legendary Lost Sectors). Public Events like Altar of Sorrow, Blind Well or Seraph Tower are possible if Blueberrys are there (There won't be any Problems to find Blueberrys, there are enough).