Thank you all for the responses. By process of elimination, I think the problem is the connection to the express in between the extreme and dock. I bought another express and tried it at dock, no luck, I then replaced new express where the one is between

Question

I have an airport extreme and express setup. My extreme is in my 2nd floor office with windows facing the water. My dock is about 250 ft away down a very steep hill. I have the express about 100 ft down the hill in an electrical waterproof box attached to a tree as high as I could install. The signal is weak and I'm thinking I might have to buy another express. Any thoughts on the best setup for me. I ultimately want to control speakers(hard wired in) down at the dock with my iphone. I have a receiver coming with airplay built in.
Thank you all for the responses. By process of elimination, I think the problem is the connection to the express in between the extreme and dock. I bought another express and tried it at dock, no luck, I then replaced new express where the one is between extreme and dock, no better. I unplugged the express between extreme and dock and there was no difference. So I believe I am connecting to the airport express or extreme that is inside the house. Again because when i approach express that is halfway I reconnect. so if you can understand my chaos, I believe the express in between is not really connecting to the extreme inside my house. Yes, No? So I need to know how to know if the express half way down the hill is getting the connection from the the extreme in the house. This is wearing me out!!!!!

Answer 1

You are asking several different questions. If you need to store your photos, music, and movies on an external volume, you certainly can. Any externally connected hard disk drive will work, connected either directly to your Mac or to your Time Capsule as a shared volume.
You should not rely upon using that as a backup device though. Although you certainly may use it for both purposes, it is a better idea to have dedicated backup devices for a variety of reasons not limited to redundancy. You would not want to simultaneously lose all your pictures as well as your backup. If they are all on the same device, that could happen. Furthermore, a backup cannot back up the volume on which it is running.
As for adding an Extreme or Express, using its LAN port for your iMac, and then enable Internet sharing so you can effectively use the iMac as a "hotspot", you can do that too, but I am unclear on what benefit you believe this arrangement would convey for you.
An Extreme's Guest network is separate from its Main network; that is the reason for having it.