The length would normally finish about knee level to show off the underdress. The sleeves can come in many varying shapes.
If the sleeves have a wide opening at the wrist either line the sleeves or use French seams to make them look more professionally finished.
A belt would be used to pull in the waist and to hitch up the skirts if long. A head rail or wimple would also have been worn.
If you wished to give the outfit a more fitted line, lace up the back from the waist to the neck with eyelets and leather lacing. This will pull the dress closer to the body.
To do this simply line the back seam. Get two thin pieces of scrap material a little bit longer than the seam and pin them to the good side of the seam. Stitch them down, turn inside and sew a finishing stitch to stop them turning out. This will finish the seam and make it re-enforced for eyelets and lacing.
The underdress and overdress would never be made from the same material and the colour most often varied. Undertunics were often cream or pale colours.