Many virgin tourers seem quite willing to buy the best upfront, without even knowing if touring will be their 'thing.' Nothing wrong with that if you can afford it. Can be quickly sold if cycle touring doesn't turn out to be nirvana.

Your approach seems sensible and practical. Do your first tour with minimal investment. 10 Wheels ideas are good. Learn the ropes and get a handle on your personal preferences/needs. If touring looks like it'll be something you'll want to continue, you'll be an educated shopper for bigger/better/lighter/more durable.

Actually you can make do on a short tour with a rear rack, some stuff sacks, and bungie cords. All you'll need can be bungied to the bike somewhere. Not as elegant or convenient as standard panniers, but can be made to work. Especially in the summer.

Rule of thumb: If your gear weighs more than about 35 pounds, you may be packing too much. That's excluding the weight of panniers and water.