Yes you can parameterise the 'ThinkTime' within the script. bearing in mind that whatever you have set up in your profile will be ignored once the bdf parametrisation of the think time has been manually coded.
Again the iterations of the script is entirely up to you, whether you do it through the project profile (workload model type) or manually (in your script).
hope this helps.
P.S. to other who might read this post... please correct me or add to if i haven't got this exactly right.
Right.. Iteration can be controlled either when declaring the Transactions (e.g. TMain or TLogin) or by creating a loop counter within the TMain. Typically Thinktimes can be changed through Active Profile using any of the following logics:
Ideal Normal distribution
Negative Exponential Distribution
Normal distribution using "normdist" function