That's possible. Open up the Hotkeys menu, go to the Global tab, expand "Control Groups", and scroll to the bottom - there are ten entries for "Add to control group", change them from shift+# to space+#, as such:
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As per the keyboard, the only mechanical experience I have is my Ducky 9008 with browns. It's pretty much the opposite of what you're looking for - it isn't tenkeyless, and it's pretty hefty.
I'm thinking you should check out the Classifieds section for MX brown keyboards, and, based on photos, decide which one fits the need (and budget).