The challenge with sales is that if you are capping your income out on overtimes as opposed to new clients you may face a paycut down the line.
While the pay disparity between what you are making now in sales vs what you might maek in management I might suggest this.
Work for another year in sales and work hard while the finace is in school. Before she gets out of school, if you like the challenges of management take the pay cut. During that year that your income is dopenw and your girlfriend is in school go ahead and get preapproved as a first time homebuyer. Your income will be low enough to qulify you for many state and federal programs. Could be tht your income goes down but your net at the end of the day is not that dieffernt if yopu play it right.