my 2c.
open world rpg is pretty ambiguous, and definitely not something you want to create as your first game or with a small team, let alone yourself. skyrim took 100 people around 3 years to create. a team of 10 would take 30 years to build it, a** team of 1 is 300 years**, you get the point. you could scale back to doing 10% of skyrim with one person and its still 30 years work.
a first person shooter template with have, well, first person shooter stuff in it, not medieval hack and slash stuff. the stats in an RPG are one of the easiest parts to create, its the NPC dialogues and quest systems that will take the longest,(as far as game coding for RPG’s go) i would suggest creating the stats yourself, it took me around 2 days to create mine with over 20 stats, exp levels ect. that will give you a good foundation to build the quests.
taking prebuilt systems and trying to adapt them to your game needs without having the knowledge to have built them in the first place will make you pull out more hair than you have on your head.