Conditional Formatting based on a date + 4, + 8, + 12, + 16, etc.

Basically what I am trying to do is create a way to manage patient scheduling based on several criteria.
• Patients must be scheduled within 14 days on either side of a specific due date, hypothetically the date is in A1
• Patients must be scheduled on a day when they would normally receive a home infusion (every 4 days)—so the appointment has to fall on a multiple of 4, based on the last known home infusion date (I’ll call that A2)

I’d like to be able to put a dates into A1 and A2 and have the corresponding calendar conditionally formatted to highlight all the days when infusions would have happen (every 4 days going backwards from A2) and all the future possible infusion dates (every 4 days going forward from A2).

It also has to highlight all the dates within 14 days (not weekends or holidays) of the date in A1 and then further identify the dates where both conditions are met.

There are some other fancy things I’d ideally like to include** but the part that’s really stumping me is the conditional formatting for a date, A2+all dates that occur in 4 day increments (and the reverse). I’m not sure that makes sense, but I did manage it by creating a zillion formatting rules, basically: =$A$2+4, =$A$2+8, =$A$2+12,…,=$A$2+364 (each as its own rule)…. and then I went backwards through =$A$2-364. Technically it works, but it’s really clunky and not at all what I wish it was. I’ll live if there’s no way to make one rule that covers all the needed days, but I’ll be bummed.

** Other things I’ve figured out how to do, but probably didn’t do in the best way:
- “questionnaires due” in A3 of example sheet needs to be visible only every 4th visit, starting at visit 17
- Last Known Infusion Date and Visit Due Date should be formatted to stand out
- Future visits (every 12 weeks) should appear, if they take place in that calendar year. I tried to go out through 2018 but Excel kept crashing so I dropped it
- The number of home doses that need to be given to patient at visit (aka how many times will they take medicine, if they are supposed to take it every 4 days)

I’ve been tearing my hair out over this and was close to just giving up and leaving it in all it’s un-elegant glory but I don't want to do that at all. Any suggestions at all would be appreciated (should also note that I have a decent grasp of conditional formatting but nothing to brag about. At all) In the attached file there are three versions, the first is how it stands now, the second is just a copy with the important rules removed, the third is stripped down so that my references to A1/A2/A3 made sense. Obviously in the first two, they don't match up.

Thank you thank you thank you thank you thank you