Re. #1: You need to encode the combinations of the stimuli / items you want somewhere. You can use <list> elements to do that. Many examples for that can be found in the forum, and a simple example using just <text> elements is provided in the documentation's "How to present stimulus pairs" topic. The same logic applies to using <picture> elements and/or <list>s to pair your items.
In the original, there are two types of trials in the experimental block, Alcohol and Filler:
<block ImageDotProbeTask>
/onblockbegin = [values.task = 2]
/trials = [1-80 = noreplace(
Alcohol, Filler)]
</block>
Each of those is run 40 times, in random order, for a total of 80 trials. Depending on how many items or items pairs you have, you may need to increase the trial count and/or introduce additional trial elements (use the existing <trial> elements as a model to create new ones).
Both <trial Alcohol> and <trial Filler> present two stimuli (<picture> elements).
<trial Alcohol>
...
/ ontrialbegin = [trial.Alcohol.insertstimulustime(
picture.AlcoholTarget, values.fixationduration)]
/ ontrialbegin = [trial.Alcohol.insertstimulustime(
picture.AlcoholComp, values.fixationduration)]
...
</trial>
the *target* stimulus and a *comparison* stimulus.
<trial Filler>
...
/ ontrialbegin = [trial.Filler.insertstimulustime(
picture.FillerTarget, values.fixationduration)]
/ ontrialbegin = [trial.Filler.insertstimulustime(
picture.FillerComp, values.fixationduration)]
...
</trial>
It is in those picture elements where you need to enter your items and pair them according to your needs.
Re. #2: You need to adjust the <trial> elements' /isvalidresponse and /iscorrectresponse attributes to also allow for the spacebar response. For example
<trial Filler>
...
/ isvalidresponse = [trial.Filler.response == values.responsekey_left || trial.Filler.response == values.responsekey_right]
...
</trial>
considers responses as valid if they are either equal to the scancode stored in values.responsekey_left OR to the scancode in values.responsekey_right.
To also consider the spacebar (scancode 57) as valid, you change that to
<trial Filler>
...
/ isvalidresponse = [trial.Filler.response == values.responsekey_left || trial.Filler.response == values.responsekey_right || trial.Filler.response == 57]
...
</trial>