One gallon may be a bit overkill, especially if you have a stir plate. Do you have a stir plate? Check your numbers. Sucrose is a BAD idea for starters as sucrose-started beer yeast will not be as apt to attack the maltose once pitched in the wort.
According to the BrewersFriend.com yeast pitch calculator which I've used for years, for a 5 gallon "High Gravity" 1.072 ale you ideally need about 331B yeast cells. So 3-4 vials of WLP, or a 2 litre starter of 1.040 wort on a stir plate.
You can make a 1.040 wort with 8oz DME and 2L of water ahead of time.
Alternatively, during the brew day, you could pull 2-4L of wort early in the boil, dilute down to 1.040, chill the starter sample, oxygenate & pitch yeast, then add it to the wort 8 hrs or so after you've racked the chilled wort to the fermenter. The starter should be up and running (i.e. replicating) by then. Hold off on oxygenating the fermenter until you're ready to add the starter. I do this all the time with summer-brewed lagers because I can only chill wort to 60* in the warmer months, so I put the fermenter in my keezer overnight until it's at a suitable lager pitching temp of 45-50 degrees.
As others have rightly indicated, you may stress the yeast if your starter is much greater than 1.040, hence the dilution advice.
If you don't have a stir plate, consider doing at least a 3L starter. Just be sure to oxygenate the starter well.