You can go so many ways here, as HOD is very flexible.

Beginning with 3 HOD guides may be a challenge, but then again, LHTH is very easy to teach (only taking 20-30 minutes tops), and so is LHFHG (taking only around 1 to 1 1/2 hours). Bigger Hearts will be the bulk of your teaching time and is an important guide to teach to its fullest. We are loving it right now! We are doing BHFHG, LHTH, and RTR and finding our year to be very manageable, first because HOD writes guides to be easy to teach, but second because my dc are accurately placed. They can do 100% of what the plans ask them to do, which makes everything flow smoothly.
You may want to start with just Bigger Hearts and LHFHG, and then add LHTH when ready.

This would be an easy way to begin for a few weeks to a month, and LHTH can be added in then after a routine is established.

Teaching guides back to back is more of a personal thing, and I have to say especially as the guides get higher up, I don''t think it would be a very big deal, as teaching time becomes more minimal. I'm on my third time through LHTH, and though my trips weren't back to back through it, I am still thoroughly enjoying it. Each child has been different to teach with it, and that's been fun to see develop. HTH!
In Christ,
Julie