Welcome back! I'll try to answer what I can.
Questions:
(1) RHCP for the V and U Yagis? Any reason to have switchable polarity?
Some LEOs have different circularities for different transmitters. For example, AO-51 has both LHCP and RHCP on 70cm. The sense can also change during a pass depending on spacecraft orientation and squint. Switchable polarity is well worth it in my opinion.
(3) Will next gen ham satellites have S-Band downlinks?
Yes, and AO-51 has an S downlink now, usually about 1 week a month. P3E and others will have S.
(4) Will next gen ham satellites have L-Band uplinks and/or downlinks?
Yes, and AO-51 and CO-65 use L now also. Kiwisat and P3E will have L also.
(6) Are these the satellites currently available for 2-way QSOs? AO-7, AO-27, AO-51, SO-67 & HO-68. Did I miss any?
Off the top of my head, add ISS, SO-50, VO-52, FO-29 (due to return soon), NO-44 sometimes, CO-65 for a real digital challenge. Lots of one-way cubesats that can be fun too.
(7) Any pattern to when AO-7 is in Mode A and Mode B?
Right now the satellite is in 24/7 illumination, and the onboard timer switches modes every 24 hours or thereabouts. Check http://oscar.dcarr.org/ as a quick way to figure out which one is on right now. When it returns to eclipses, it generally favors B and only works while illuminated.
I hope that helps. Joining AMSAT if you're not already a member is a good way to support the program, and there is always something interesting in the AMSAT Journal. There are several active ops in your immediate area, including a BOD member; they may chime in. See ya on the air soon.
73, Drew KO4MA