Normally I'll wait longer like close to a month after planting. But because its growing so fast I'd say go for it. Just cut it tall.
Yes the just take enough off to make it look nice. I'd say for the first 2 or 3 mows cut it 3 or even 3.5in.So if it's average 3.5 inches when i cut it, cut maybe just down to 3 inches, then do exact same thing again a few days later, and then go down to 2.5 inches and maintain it there?