Is there a way to allow for short answer questions of type \AMCOpen in a text file?

Currently not, but I think it is possible to add this feature

2) Is there a way to format tables?

Not yet.

I am supposing latex will do this (though not it's strong suit), am I correct?

Yes. so in fact you can use the local LaTeX tags (all in one line):

[[ \begin{center}\begin{tabular}{|c|l|} \hline water & 0 degrees \\ \hline polystyrene & 160 degrees\\ \hline \end{tabular}\end{center} ]]

3) Is there a way to include graphics?

Yes, with something like

![height=7mm]imagefile!

to include imagefile.png.

Thank you for your quick response!

You suggest in your response to (1) that the feature could be added. Is there a possible time frame? Note: I recognize that this is probably not high on your todo list.

From new revision r1326, you can use open questions from AMC-TXT with something like that:

L-OpenText: [_[*Please write the answer on the separate answer sheet.*]_]
L-OpenReserved: [_Reserved_]

[...]

*<lines=4> Describe the moon.
-[O]{0} O
-[P]{1} P
+[V]{2} V

Here, the examiner will have to read the answer and then tick one of the three boxes to give the student 0 points (box O), 1 point (box P like partial) or 2 points (box V like valid).