If you brew it as an ale, you can probably skip the secondary altogether. Count on 3-4 weeks primary for this big of a beer. The FG should be below 1.020 when done, but possibly it will stop at something a bit higher than that. You want to see two equal measurements a couple days apart before bottling. But even if it's done early, let it stay for 3-4 weeks. The yeast will still be improving your beer.