Welcome to the fun board of 'quilt nuts!' You asked how much fabric to purchase? I would purchase no less than 3.5 yards for the background fabric (based on a double bed quilt) the if you have 4 fabrics total: 2 yds. of the next must used fabric; & 1.5 of each of the rest. Of course; you just gotta get some other fabrics too if you maybe 'need' them! I find that if you buy a little here, a little there, great way for building! You will find that you have some fabrics left over too after making a quilt! NEVER throw out any that is at least 1/8 yard.
BUY when there are good sales - build using COLOR! Colors you love & cannot do without. Always get minimum of 1 yd. You are so lucky to have a suportive husband!