upd I play on a PC and I also plan to administer the server for a PC)
Hi and welcome to the forum. I think you will get here all informations you need. I can not answer all your questions. But also I have one what would help people to give you the right answers.
Do you play on pc or console? Of pc you have the freedom of many cool mods. I am sure for most of your wishes there is a mod.
As console player you are limited to the basegame and have no access to the game database.
But let me try to answer this from my console perspective.
I had more than one account on my Playstation for this. On Playstation it’s easy you can create and account and all your games and your ps plus are active for the whole console and it’s accounts.
I had one for admin jobs… For example wiping Chinese walls on the noob river.
Other accounts where for building community buildings or ‘pvp dunguen events’
I wish the vanila game would offer this. I would love to see a solution like the battle standard. A pve flag that can only be placed by admin.
Unfortunately there is no way to do this.
But I am sure there is a mod that gives you what you need.
Don’t know exactly what you want to change? Style or behavior? I think here you need a mod again.
You can only spawn npc as admin but the are gone when die or server restart. (server restarts a recommended once per day)
As console player it’s your only choice. I had good experience with the customer support from g portal. Can’t say anything bad about them but I think there are many other opinions here at the forum. What I read about it is that g portal is not good for high populated servers. 20+ players and the server lags. I can share this experience only on officials and if there are 30 players online its horrible. But more than 20 players happens maybe once an year…
If you play on pc you can start your own local server and just play around with settings and mods to create your world before buying a server.
In my ps4 experience, gportal was responsive as well and I never had an issue either. On pc, I just host my own on my own local machine using the dedi launcher. So I havent had any complaints about the provider there either 
@Warlock_1115 People are definitely going to need more information on console Gportal is your only option. Not much in the way of options to change things. Are you going for pvp pve-c or pve. We have had a 20 slot for years players character does not stay on server when logging out I have wondered if maybe that takes a load off the server. Anyone have a opinion on that. If not playing pvp no reason to have bodies laying around. 
It might have a small effect because of the inventory, but probably nearby inventory is going to make a much bigger difference. I would expect it to be in the noise unless there were 100s of bodies lying around, all with full colons of stuff.
I will try to give you some suggestions without mods.
We do not own the building pieces that devs fixed the npc camps and towns, just decoratives. But dlcs provide unique building pieces and you can create small areas (villages, towns) that others can “raid” and steal. The key to this is an “alternative account” , that you will enter and build without creating issues to the original management of the server.
On vanilla game, so far, the admins are placing rules. If you wish on your server to have a no raid territory, you have to name this territory on your rules. Players must respect or ban.
On vanilla no, you can spawn as much as you wish however and choose from the random characteristics the ones you wish. If you wish to have “thralls” with tremendous hp you can spawn witch queen, they come out 70k if i am not mistaken and if you lvl them up they reach over 110k. So the raiders will find issues against 30 thralls with 110k hp 
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Not the worst i can say!