Well for combat mechcanics, i suggest you'd might wanna try having 3 main ones, (slash, stab, whatever) but maybe add one or two attack combos so the players wont have a hard time learning to fight and they wont be too bored. If you wanna make ombat mechcanics for bosses, i suggest they have TWO adifferent animations for the same attacks, so it would be diffucult for the players to guess the attacks, because most players beat bosses easily if they can learn the boss's attack pattern. Basic type of game you can start is like a quest, like maybe you have to defeat something or rescue someone. For items i'd say you could make a trading system, like some items you can only get by trading, and some items are key items to a sidequest or something.