I got the train to Mosen and geared up on a bench in the Seeblick campsite. There are toilets and showers available to campers there.
I chose the nearby Mosen ferry pier as the start-finish line for my loop. From there you can follow the yellow Wanderweg signposts the whole way around. Just disregard the ones marked with a ferry icon instead of 'Wanderweg'. The lake is dotted with swimming spots, barbeque areas and campsites, which can be busy in summer, but crowding was not a significant problem on my attempt. Note that despite the published FKT route going directly along the coast through Beinwil am See, this path was locked on my attempt, and most maps show it as restricted access. Expect to divert around the sports grounds, as I did.
Almost the entire loop consists of smooth but unpaved trails, or gravel roads. In the southwest corner of the loop, it's very slightly more untamed and undulating. In the dry it was no problem with road shoes, but a bit harsh on exposed foam, so spare your race shoes if you're precious about them.