Is it possible to use Numbers like 1-10 ? instead of 1/2/3/4 ? 

Also; What if i dont list an items rarity do they become just extremely common or ?

Like barrel components / pipes/springs/ blades/rope etc.. what should i make these rarities?

Maximum rarity you can set is 4 which is extremely rare.  i only use rarity for crap i dont want to be in the loot,