Honestly, the plan can be as short or long as you want it to be. I think the real decision is less the length of the plan, but more so how much do you want to improve? I think answering that dictates the length of the plan more. You want more gains, then the plan will likely end up longer. With that being said, the week of 7/17 is 14 weeks from race day and that's plenty of time.
We can certainly make anything work. I think you'd probably have to choose an either or (especially since the HM happens first) as an "A" race. It sounds like the 10k is your "A" race, which means we could incorporate the HM as a long run pace or slower type run (dependent on a myriad of factors that go undetermined until it's written). The plan wouldn't look to dissimilar from the HM plan you followed except the pacing would change focus on a few of the runs throughout the plan. But mostly, endurance is still the predominant focus of the plan, even when we hone in on true speed pacing. Although, to be fair, working on speed pacing in the summer will be tough. You know with the

and all.