A compromise could be 4 Watts (ish) from MEO. Here's an oldie but goodie..... http://www.g0mrf.com/MEOSAT.htm
Yes MEO would be good. It should be possible to improve the signal levels while keeping omni-directional antennas on the satellite by using lower frequencies bands.
A 144 to 50 MHz (if we can get an allocation there) transponder or 144 to 28 MHz would have a significantly reduced path loss on the downlink (8 dB ?) compared to 435/145.
73 Trevor M5AKA