Thanks to all who helped. I finally did book everything in business class but went a completely different route.

Am now going outbound YYZ - LHR (on AC) - ZRH (on LX) - BKK (onTG) - SYD (on TG) and return SYD - BKK (on TG) - ARN (on TG) - LHR (on SK) - YYZ (on AC) , all business class.

The only thing I would have preferred is some better planes on some routes for business class, but did not want to spend the extra 80K miles to upgrade a few segments to first. Seemed like every other route, including LHR-BKK only had economy available for some of the longer segments.

Will be nice, have a stopover in ARN on the way back to get a massage and a little break on the way back.

Any advice on lounges / transferring in any of those airports? No real long layovers, all between 2 and 3 hours.