Will try to answer your points by number.

1. The rules changed a couple of years ago to add lines 24-28 in your star file reference, prior to which it just said "unlimited changes allowed" for tickets obtained in Regions II/III. So I would cite the rule (available on the Oneworld website in a .pdf file) and hang tough on your re-timing.

2. Edited. I had a long-winded version of "don't think so" written but have subsequently become unsure. Don't think so, but asking is free. I DO know they won't put it in a ticket issued today, but getting it added in a re-issue once the route has been inaugurated, maybe.

3. You're probably cruising for a re-issue sooner or later anyway, so I'd pick one of the less desirable but more reliable year-round route alternatives and go with it, then re-do it at re-issue. You can always try to be persuasive however. (This is in reference to DFW-ANC and LAX-SJO seasonal conflicts.) I wouldn't go to SJD but that's a personal preference (I can make big margaritas more cheaply at home.)

4. I haven't had any trouble increasing the total segments to 20 after starting out as an e-ticket, but it's anybody's guess how "smoothly" the transition from 20 > 16 will go. If it were me I'd bite the bullet and have it done as a paper ticket, then have it re-done as an e-ticket once you've burned 4 segments, if they'll let you. Note a paper ticket re-issue by anybody but AA will probably result in a machine-printed ticket, but one that AA may not be able to see an image of in their system.

One thing about open dating is that the tariff people assume every possible stopover point is one, so the full fury of airport taxes etc. is added. Getting them stricken later when a re-issue eliminates the justification for the taxes is rather more rare (but I have had it happen.) Set against future fuel surcharges, though, I'd be happier paying todays taxes and YQs rather than next years. YMMV. Myself, I'd just do dummy dates for the whole thing and avoid the pain later.