I realise I'm probably asking a stupid question but how do I sell a property through a vendor and stop players entering the place before they have bought it.

The vanilla homes have a locked (level 100 - requires key) front door, and you get the key when you buy the property. That level of lock can't be picked.

The property is one i've made up, but its a bit big to just get so I want to have to buy it for 120k.

Also wondering ho to add staff to the property,

1 x Captain of the guard, (can be a companion)
3 x Guards (Can be companions)
1 x Cook
1 x Butler
1 x Blacksmith
1 x Alchemist
1 x Gardener
1 x Stable master

Need all the staff to have full daily plan & work shedule.

Can anyone please tell me how to do it.

That's very ambitious. First create all the NPC's and AI packages and place them where they need to be. There's tutorials on the CS Wiki, or follow the link in my signature.

Then look at the existing scripts for the current houses for sale to see how to set up a script to "buy" the house. You can make each NPC a separate buyable item even, like the vanilla houses where you have to buy each room.

thanks for the help will give it a bash now, could be some time.