how much elevator control force is
available with and without trim being set.

It depends on the system.

For example, if you have a trim tab, the tab is reducing the amount of
force needed to go one way, while increasing the force needed to go the
other way; the net effect is the position of zero force (corresponding
to the trimmed airspeed) is different. The elevator "wants to" be in a
certain position, and if that position is (say) near the nose-up limit,
then it will take less stick force to go to the full nose up elevator
position.

In the case of an auxilliary elevator, the nose itself is moved by the
added forces that the auxilliary elevator provides. This does change
the angle of attack of the regular elevator, but only to the extent that
it is "trailing", not to the extent that it needs to provide any extra
force to move the tail (and thus the nose). The elevator will trail in
(say) the somewhat nose up position (corresponding to the trimmed
airspeed), and less travel will be available in the nose up direction.
It will take less force to get there however, since the neutral position
is already trailing somewhat nose up. Other systems have their own
methods, but if you see it here, you should be able to figure it out there.

IT is possible that a fly-by-wire system could be designed without trim,
relying on brute force instead (and using software to give the stick
feedback, if desired). In this case, the force the pilot feels is
arbitrary (up to the software designers) and the force on the elevator
is just what it would be were you to muscle the elevator around.
"Trimming" would move the elevator just like the stick would, and you'd
be left with less travel in one direction and more in the other, but
mainly because "you're already there".

but it still
reduces control in one direction. Could be a big issue during landing
during gusty crosswind conditions, or during takeoff when unexpected
turbulence is encountered.

Well, yes, but this is taken into account when they designed the
airplane. Every limit, when encountered, will be (...er) limiting. The
aircraft is designed so that those limits are outside the normally
expected flight regieme, and gusty crosswinds are part of that regieme.
Alas, airplanes are not really tested for this; the "demonstrated
crosswind component" is not considered a limit - it is just the maximum
crosswind that happened to occur when they test flew it (or maybe test
flew it for FAA demonstrations).

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
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