I'm planning to rent a C100 to try it out for shooting soccer and other sports, primarily. The 70-200 lens was recommended but I don't think it will have sufficient reach if shooting from the stands. Any other lens suggestions, also any other tips for shooting soccer with a C100?

Canon 100-400mm! Love it for sports!

Try it with a 1.4x or 2x extender.

18-135mm !

Depending on timing (it seems the first C100 mkii unboxing video has just hit the web) then I would suggest you try and hire this newer version.

Why? 1080p50/60 would be very, very useful for any sports coverage and also gives you some nice sharp slow-motion options in post (on any clips you want that effect on).

I have a C100, Canon 70-200mm F4 IS and a Canon 1.4x Converter (Version ii). I find it nice and light for even quite extended hand-holding. Usable long reach shots are just about attainable with practice, and the IS makes a big difference, for sure. But of course, where you can, I would definitely use a tripod with a decent fluid head (I have Vinten Vision 3AS system which is excellent). If pushed, a monopod woukd be a good fall-back.