Stats

STR- How much you can carry & attack

CON- Frail, fragile, put in weak constitution in google & got that... Makes sense so I say that means defence physical/magic.(I was kind of thinking make every one have 100 hp/stam. in game & just that is what they have)

AGL- Speed

INT- How much you can learn & magic attack/power

DEX- How good you are with your hands

Crafting

I Think Martel Online has a awesome sounding sys, try out resources & make a unique item

Gathering

If you cut a tree it falls. mine a rock it crumbles & harvest a plant it disappears (Conan exiles(

Loot

Animals don't have gold, weapons or items if you want loot harvest with a skinning knife to get skin, a butchers knife for meat/bones, humans might have stuff in inventory & WYSIWYG if you see it on them, they die, you can loot it

Building sys

(Conan Exiles) Build freely, make buildings look how you want

World

destructible

PvP

Free for all, Full loot & no safe zones

Have you tried ARK?

Just now, Nypyren said:

Have you tried ARK?

No

Mortal Online is almost there, they just need some bugs fixed, I wish I had the $$ for the rights so I could tweak it some... I really love the thrall sys from Conan Exiles, that would be awesome in MO...

free for all - 

need serious repercussions for actions to prevent griefers taking over your game (particularly if their is skill/weapon ramps which make players overpowering to newbies  (even that isnt enough if ganging up 2 on 1 is more than sufficient for quick kills on a newbie)

unless you want the game to be like the typical Multiplayer combat type games (fight-die-comeback to life endlessly) an awful lot of careful play design is required. 

destructible ...

terrain (of any detail) has an update problem (player moves into area that has changed then all the changes have to be transmitted to their client - particularly bothersome if they are cumulative.  

LIkewise if players 'can build stuff (as in terrain objects)' then something has to prevent other players destroying whatever - even faster - just for the hell of it (more griefer activity)

do some research into limitations most MMORPGs have in them to nerf/limit/homogenize just about anything players can do to each other.  Likewise on communications limitations that non static worlds require

I like the sys conan exiles has, it is not that hard getting on your feet again... Mortal is a bit to much a pain in the butt... A blend of Mortal & Exiles sounds interesting really, as for the repercussions. hmmm... Darkfall has a good flagging system, griefers become red, mortal you can target a griefer & have a guard attack... Reds are attack on site for guards would be good... Plus put the security level of the area you are in like Eve has in... then mark the map of the safer areas,,, Plus, the graphics should be good, but no need for OMG want it to be able to run good on systems a few years old...

This post is very wide. You ask about ALL aspects of MMORPGs and then suggest some rather standard solutions. Exactly what stats you should have and what they do is on a detail level. Where are you in the design process? Just philosophising about games in general? Maybe try to come up with more precise questions important for your project.

I agree greifing would be a big problem (given the impression from your first post). If this isn't handled well, your game will be empty pretty soon.