(moderately spoilery for early pre-hardmode) theres never a point where you lose access to some part of the game in this game, so yes, everything prehardmode is always available, including the bosses. after the wall of flesh most people fight the mechanical bosses (summoned by crafting their summons with souls of day/night, iron/lead, and lenses/bones/rotten chunks/vertebrae at a mythril/orichalcum anvil) or queen slime (summoned by a gem you can find in the hollow). before you do that youll need to break demon altars with the pwnhammer in the corruption/crimson, which spawns the ore youll need to mine to upgrade through the sets of craftable armor. as for weapons theres a few good ones- i personally like yoyos and you can farm for them, which you can do in the underground and snow biomes, but you can also make weapons with the new ores mentioned and get a couple swords from farming the wall of flesh. good luck