No. Cash Wanna Get Away fares are nonrefundable. You will get a credit which will need to be spent within one year of the date that you bought the ticket (not one year from the date that you intended to travel) if you make changes to your travel that results in a difference in price that favors you.
If it's your intention to use RR points to pay for all of your airfare, then you should wait until you have the points in your account. If you plan to partially pay for your trip with RR points, then book the cash tickets whenever you feel comfortable with the price and then book the remainder of your travel with the RR points when you have enough to cover your fare.