We wish to use LimeSurvey to present customized intervention questions to research study participants. Ideally we would like to design a survey with multiple question groups and be able to show a targeted question group to a user by using a custom URL which will open up the survey and present the user with the first question of a particular question group. Is this possible?
Alternatively, we will create a set of small surveys each with a single question group and a set of questions within that the group.
Any advice/comments would be much appreciated.

I assume that you know the participants and what question groups they should see. In this case you could work with tokens and custom attributes. Based on the attribute you could create conditions or expressions, that will hide the non relevant questions for this specific type of person.

Yes we do know the participants and we have logic to decide which question groups the participants should see. So it looks like we could create a set of tokens for each of the users and then create a URL with the "/token/{token}" appended to the end of the URL for the active survey. This will give us the ability to present the survey to an authenticated user. I am not sure how we would pass in custom attributes in as part of the URL to cause a jump to a specific question group. Are there any examples of how this might be done?

Additionally, am I right in thinking that - If we wish to force the user to see a question group multiple times, we will need to create a unique token for each repeat visit.

You'll find more information on tokens and how the work here:
www.limesurvey.org/manual/Tokens

And in specific the custom (user defined) attributes:
www.limesurvey.org/manual/Tokens#User-defined_attribute_fields

So you would create a token field that defines which questions groups a person with a specific attribute value can see. E.g.

Everyone who has the code "A" will see question group 1 and 2, everyone who has the code "B" will see group 3 and 4 and everyone who has code "B" will see group 1 and 4. Then you would create the conditions or even better expressions for each question group in your survey and hide or show the question group, depending on the attribute value.