For #1, I'd go for a pair of firemouths, pair or small group of rainbow cichlids, a group of green swordtails for the top water (possibly), and possibly a third pair/group of some kind...maybe cutteri? These would all be CA cichlids/similar source. If you put in enough rock/wood structure to allow breeding spots these should be fine. I kept two pair of thorichthys aureums (similar to firemouths) in a 55g and they bred regularly (just one of the two pairs, though).
For #2, I don't have suggestions but Ron's was good.
For #3, if you go Tangyanikan, you could go for a pair of leleupi or the calvus/compressiceps in one rock pile on one end, some larger julies (not transcriptus gombe or dickfeldi but probably marlieri or regani) in another rock pile on the other end, some shelldwellers in the middle (leave an open space). Possibly even some paracyprochromis nigripinnis if you stack the rocks high enough...cyprichromis in that tank with the other groups might be pushing it, but it might be an alternative depending on the height of your tank.
For #4, I had great success with an African brown knife plus bichir(s), but those are both African riverine species. Black ghost knife would work well with anything that won't be too nippy (a single large cichlid is probably a bad idea, but a group of several would be OK so that they focus on each other vs. the knife), and that won't intrude too much on the knife's space. Maybe a group of angelfish, and go for 2-3 pairs? The knife would eat any fry you get but they would be compatible in terms of biotope.