In all that discussion about pier heights, I suppose you have considered
that in the end it might be preferable to have the AP1200 saddle at a final
height, such that you can flip the OTA in, from "no more than" a shoulder
level. Otherwise, you might be looking at back strain. Of course, this is
assuming you will take the OTA down for star parties, etc.
When your AP3600 eventually arrives, it will of course be taller than the
AP1200, so it might be more difficult to remove the OTA from it, for use with
your (portable) AP1200 in the field.
Don't know how you were thinking about the changes, but one idea might be
to consider a small (but wide) portable one step platform, that could be
brought upto the pier when needed, for such tasks. Then again, with the
AP3600, it might end up being a permanent platform, for comfortable viewing
and reaching attachments.
Plan ahead ...