I do a lot of RTWs where I stop in each place for only three days. If it's our first time, it's enough to get a feel for the place and if we want to go back, and if we've been before then we know where we want to go. But that's based on doing an RTW each year.

Expert Flyer has a timetable query that's very helpful for this, although if you have a date range in mind, then the flight availability query works fine. For advance planning (more than 331-360 days ahead), I'll pick dates in the same month a year earlier, to get an idea if flights might be seasonal. The timetable query includes the start and end dates of a flight (although these may be extended). When using the flight availability query, as mentioned the "alliance" drop-down allows limiting to OneWorld flights. When using the timetable query, use the filter in the results window to deselect all airlines, then select the OneWorld ones. Be aware that in some cases, a flight may be available as a OneWorld airline code but operated by a non-OneWorld airline. Such cases might not earn anything, check the details of the frequent flyer program you will credit to.

I always go home at least once on an RTW, often twice, on occasion three times.

I agree, although I place BA pretty far down, because of the risk of getting their old Club World, which are dreadful seats.

This is a great option, although as i mentioned, stopping anywhere in the U.K. for 24 hours or longer will incur the UK APD, which is expensive. You might consider stopping just outside the U.K. (e.g., DUB) and taking a side flight or even surface transportation, although I personally never want to waste a segment, so what I usually do is to pick a place I'm stopping anyway, and get positioning flights from there to my home and back. E.g., on my current RTW, I originally planned to stop in DOH for six months, with positioning award flights from there to my home and back, but QR has dramatically reduced business class award availability, so instead I moved the six-month stop to LIS, and purchased a business class round trip from there to the U.S. and back. (It cost about half of what the same trip from the U.S. to LIS costs.)

This is an excellent point. One thing to be aware of is that QF offers direct flights between LHR and SYD (they make a stop in SIN but it's only one segment).

How do you use EF to estimate taxes and carrier surcharges? I know some people use matrix.itasoftware.com for that, although that shows what the operating carrier charges, not what an RTW ticketing airline charges.