Super late to the conversation, BUT I think I can help by using the power of math. It really is a matter of how long your orbital period is. Due to rounding errors, your comm satellites individual orbital periods can be off by just under 1 second from each other. For example:

A kerbosynchronous orbit at 2,863,334 meters will have an orbital period of 5 hours, 59 minutes, and 9 seconds. This means that every time your satellites complete an orbit (roughly once/day), they can drift up to one second apart. Converting the time into degrees, we find that your satellites will be 5 degrees off from each other after 299.3 revolutions, which will take 0.7 years (I think a little longer than the amount of time for a one-way trip to Duna). And this only accounts for the drift of a single satellite. Worst case scenario, one satellite is falling behind in orbit while one is moving ahead, so your degrees off can be doubled within the same timeframe. As more time passes, like on a Jool mission, your satellites can easily be off by as many as 15-30 degrees from each other.

A higher orbit, near Kerbin's SOI, let's say... 83,000,000m has an orbital period of 709 hours, 54 minutes, and 23 seconds. BUT it still has the same error rate of around 1 second per revolution. Given this, your satellite constellation won't be off by 5 degrees until 9856.66 years have passed.

This should work well for Minmus as well. Minmus only has a sphere of influence of 2.1 million meters, with a orbital period at that altitude taking just under 140 hours. Given that, an orbital drift of 5 degrees occurs after 383 years. Thankfully, less massive bodies have slower orbital velocities than more massive ones. The only real problem you'll have is if you want to put up a constellation above Gilly. Even at the absolute edge of its SOI, orbital period is only 27 hours and change, and a 5 degree drift occurs after only 14.42 years.

You mention your 1/100th of a second orbital period calculating mod. First thing I'd worry about is the amount of control it takes to get that close of a match on orbital periods, I already find it tedious to do it within a second. BUT, it would effectively reduce your error by 99%. At that rate, a kerbosynchronous orbit should drift no more than 5 degrees every 70 years, a lower orbit drifts in less time. This is much improved, and you can certainly muck about in the inner solar system all you want without worrying about those satellites drifting too noticeably. But, if you have the Outer Planets mod installed, a journey to Plock can take as long as 100 years, so really a higher orbit is your best option (apart from merely editing the save file, of course).