Soo lets start:
#1. Character class/role/race?
I think the good idea will be "specialization".
All start with same skill and in time player can decide what thay want. Every spec should have some uniq skill not able to other spec
*heal - bonus to stimpacks/medpack use/skill to buff party members in battlefield. Uniq - body improvments like implants
*trader - bonus to trade better prize/more sloots/. Uniq - access to trade caravans - can transport loot of stuff
*crafter - bonus to craft items. Uniq - Research - Scientific research (plans for items/hi tech creation)
- Historical research ( able to use old map - military base/ect.)
*enginer/geologist - able to build big complex like city/mines/ect. Uniq - able to find deposits of materials like coal/iron ect.
Race :
*ghouls - good in crafts/tech
*mutants - good str/weapon
*humans - good in race relations/universal (but dont have +bonus)
#2. LvL?/Skill train? :
I think best option is skill training. Mixed with class spec it could be nice way to create uniq character. After picking Heal spec playwer will unlock special skill only for that spec.
#3. World? :
I think must be huge ( in post nuclear world 100 peps in non city location will be strange :p)
#4. Environment/NPC city/NPC fraction/Player city? :
Npc City - like in all fallout
Npc fraction - BoS/Enclave/Raiders - those npc should have not able to conquer by player teritory on map. Thay should control teritory with rare materials to craft.
Player city - Yes. I think player should have option to create your own city but ... it should be soo hard that onlly biggest guild/corp should be able to do it. And of there should be max limit for it. max 1-2 city per guild/corp
#5. PvP/solo/World/Guild vs Guild
In my opinion player need to fight for. Guild/corps should be able to cap some terriroty on map ( alasca - lot of petroleum/ect). Some of guild/corp tournament organized by BoS/Enclave/Raiders - with some uniq reward (tech/resources). I think war on teritory between corps/guild will be more fun than ganks 10v1.
Discus?