Yes and yes, assuming your second question doesn't involve a race choice (that only reflects the UI anyways in custom games), but instead an attribute value choice.
1st question: Just write a trigger switch depending on possible attribute choices and do your vision revealing/control tweaks accordingly.
2nd question: Inside the game variants window you'll see in the Usage tab an Availability section. Changing this to First Come, first serve forces everyone to pick a unique attribute value choice.
Yes and yes, assuming your second question doesn't involve a race choice (that only reflects the UI anyways in custom games), but instead an attribute value choice.
1st question: Just write a trigger switch depending on possible attribute choices and do your vision revealing/control tweaks accordingly.
2nd question: Inside the game variants window you'll see in the Usage tab an Availability section. Changing this to First Come, first serve forces everyone to pick a unique attribute value choice.