Most liquid Glyphosate products, including RoundUp QuikPRO, if kept at moderate temps in a cool dry place will have a shelf life of 3-5 years.
If only a small area of the lawn is affected by the outbreak, spray only the affected area with RoundUp Quick Pro. If the problem amounts to no more than a few spears of quackgrass in an area of your lawn, paint the individual spears with diluted RoundUp QuickPro. Becareful to avoid getting the product on desirable grass. If most of the lawn has been affected by quackgrass, the only sure fire way to get rid of it is to spray the entire lawn with Roundup. Spray when the lawn is growing actively, preferably in the spring. The treatment will kill the lawn grass as well as the quackgrass. After about two weeks, you may begin the replanting.
Roundup QuikPRO does come with a surfactant in the formulation. There is no need to add an additional surfactant.
The mixing ratio of Roundup QuikPRO is 1.5 oz. per gallon of water. This will treat approximately 1000 square feet. For a 1/2 acre, you will need 21.78 oz in approximately 21 gallons of water. This product will kill whatever it comes in contact with, including weeds, unwanted shrubs, etc. You will only need one bottle of this to cover 1/2 acre.