I love the idea of the EF-S 17-55mm f/2.8 IS USM 's low light performance (a constant bug bear), but is it too bulky for the body in everyday use?
It may sound like a cliché but no size fits all. Some people will find the lens somewhat front-heavy and unwieldy but others will cope just fine with it.
I hired that lens for about a week and it did seem quite bulky but after a few hours of using it, it felt pretty natural, especially with me using a battery grip on my 550D. I use my 15-85mm (not quite as heavy as the 17-55mm but much heavier than the 18-55mm kit) as my main lens now.
I'd love to go for an L (luxury) lens from what I hear about build quality, but these seem to be generally for full frame bodies and so compromise on wide angle shots.
The lenses themselves aren't compromised but as you said, they are optimised for the full-frame bodies (L lenses were around long before the APS-C bodies became mainstream) so most would be quite tight at the widest angle when mounted on an APS-C body. However there is the 17-40mm L to consider unless you think it doesn't have the reach you're after.
I do use telephoto a fair bit (my daughter is an athlete and capturing the action the far side of the track is a must), can I expect to get good results with the Canon’s EF-S 18-200mm (no USM and quality compromises!), or should I just save up for a second lens for telephoto work?
I wouldn't call the 18-200mm rubbish but if it is practical for you to carry a second lens and change it, it's not a lens I would recommend. I see it as a lens for those who need a wide focal range first and foremost with minimal intention of changing lenses in one sitting and are happy to sacrifice image quality and can put up with noticeable distortion (the latter of which can be corrected with a bit of post processing). If image quality is more important and you don't mind changing lenses, I would recommend looking at either the Canon EF-S 55-250mm, the Canon EF 70-300mm or the Tamron 70-300mm.