[Antennas] feed point impedance of a nonresonat verticle

[David]

For several years now I have used an end fed wire (end fed zepp antenna) But all good things must come to an end. The tree that supports the far end of the antenna is coming down to make way for a new road. So I am going to be forced to keep my antenna completely in my back yard which is 70 feet wide and 30 feet deep and surrounded on 3 sides by a 8 foot high concrete wall as is so typical of homes in this area.  My house has an attached garage that has a building on the back that is for storage and my ham shack.  My idea for the new antenna is to clamp a 10 foot section of TV mast to the outside wall of the ham shack attach 4 radials 30 feet long and spread out 90 degrees. I will then attach a 13 foot vertical antenna to the to  the mast for 10 thru 20 meters and a second vertical fiberglass pole with a wire in it 30 feet long can replace the shorter antenna for 30 and 40 meters. My question is does anyone have any idea the feed point impedance for these antennas is  and will a 1 to 1 or a 4 to 1 unun work  better?  Depending on where I mount the pole I will be using 10 or 30 feet of RG213 coax to feed the antenna.  Another option might be 450 ohm ladder line from the  antenna to the balanced wire terminals on my antenna tuner. Thank You in advance and Merry Christmas  David N5WMQ