I would like recommendations for an email client with low (and configurable) disk space utilization, for Windows. Good Gmail support is a big plus.
i may suggest Thunderbird, but no idea if it fits your bill since your requirements are still very vague...
but at least i can tell:
i have no idea about a google-support, since i don't use it and IMHO it isn't necessary at all. if it isn't induced (in a satisfying way), maybe you can find something at https://addons.mozilla.org/thunderbird/.