How many sub- issues should the ISSUE section have on the memorandum? And how many cases, statues, or rules should be on each memorandum? Also should I begin researching on Lexius.com or should I use that resource after searching in other places?
Although I'm not an instructor for your program, I thought that I'd try to address your concerns about the assignment.
Despite the fact that you will be preparing two memos --one for each of the two parties--you will be using the same format to advocate each party's position; as such, you will want to select the issues that need to be addressed. A bit of a trick is to frame the issue in terms of the position you want to take; i.e. a father has always fulfilled his responsibilities but works as a manager of a strip-club. If you are representing the father, you'll want to make the issue revolve around the fact that the father has always fulfilled his obligations and responsibilities. If anticipating the strip-club challenge, a sub-issue could be; "Should a manager of a legal business be subject to bias against his parental competency due to the nature of the business?" Whether it's the main issue or sub-issue, cite the law that seems to reflect your argument --it helps if you can cite a case ruling as well due to stare decisis.
In terms of numbers, I would say that you should look at what needs to be addressed. If the assignment doesn't prescribe a given number of issues/sub-issues then focus on what you think should be an issue or sub-issue and forget about the numbers. Remember too, that a sub-issue is raised only to clarify something that is raised by the issue. In actual intent what you're trying to do is to anticipate the other side's arguments/objections and counter them preemptively.
An internet search is a good way to find statutes and cases so it would be fine to begin your search using Lexus/Nexus. You might want to try searching the sites of parental advocacy groups as well. The sites can reveal decisions which you can then research by going to a reference library. You can then delve into the justices' decisions and the arguments presented in the case. One note of caution though. It's tempting to only select the decisions which seem to support your contention; however, if you come across two cases that seem the same but have disparate rulings, look at the reason for the ruling that goes against your argument and try to formulate a good counter as to why your case is not exactly the same. In this way, you can disarm the other side by stating; "We are well aware of the case of E. Fudd v. B. Bunny but can show why the facts of that case do not mirror the case at hand".
So, I hope that this hels a bit; however, I invite you to contact one of your instructors directly from your homepage for a more definitive answer to your questions.
Best of success!