[Suicide Junkie]

1) The sentry order is not available because your ship has the low supply warning. That is one of the conditions which clears the sentry order, among others, such as enemy ships sighted.
1b) The repeat orders button is only available if the ship has orders in its list. Order the ship to do something first, then the order will become available.

2) Eh? I'm not quite sure what you mean, but might the research minister be turning it off for you?

3) Cargo is generic. You can put whatever you want in the hold. The satellite bays let you *launch* satellites, while fighter bays let you *launch* fighters. And so on.
Troops can be dropped in combat without need of a special component, and anything can transferred between the cargo of ships and planets at no cost.

4) The design minister dosen't like people poking their noses into his work. The minister clears out and redesigns things on a regular basis.