AXIS 2.0 Rear Wheel Upgrade Recommendations, Please.

Hi guys. I've had my Specialized Roubaix Sport for three years now (bought it brand new in 2016) and my rear rim cracked near the spokes, so I had a couple questions that I was hopeful you all can help me with.

1) Is it okay to buy JUST the back rim and not the front? In other words, for whatever reason (be it a smoother ride, etc) would it be best to buy a wheelset instead of just one rim? Any pros and cons to both sides that you all can think of?

2) Is there anything I need to know before making a purchase, outside of making sure that I buy an 11-speed wheel?

3) Finally, what would you guys recommend? Would like something that is decent quality (at least as decent as the Axis), but at the same time something that won't break the bank, as I don't really need to shave off ounces to minimize weight. I just want an awesome, good-quality wheel for a good price. So for one rim, would like to spend less than $150, if that's possible. However, please do share whatever you have in mind, as I'll definitely consider anything you guys recommend that you think is worth it, even if it extends beyond my budget.

Thanks.