1) Ummm, I think Ben A released scripts where if you press a button in a trigger zone text will appear. Just a little fixing of the script and you should have that.
You will find Ben's scripts if you click this little face
2) idk... I never tried out the shop script.
3) Well I haven't looked at the shop script but I do have an idea. Make the entrance to the house locked (whereas you need a key to open it) and have the shop script used to purchase the key to open the door. That way you are technically getting just a key but in theory you are getting the house.