Love strong tea but only drink iced tea, how would this work brewed in this way?

No. It's my favorite. But it should be served hot with milk , with or without sugar. It's strong tea. For iced tea you want an Orange Pekoe tea. For some diversion you can mix a little earl grey with that along with fresh mint and sugar, which is how I make mine in the summer. The hint of bergamot in the Earl grey plays nicely off the orange pekoe and sweet mint. This has malty Assam, Kenyan and Rwandan teas. It's best served hot as a breakfast tea. Or you could add spices and make a chai tea, or even use that chilled w/milk for a cold chai tea. But for iced tea, you need a light and mild tea. This isn't it. Too acidic and strong without milk. But it is my favorite! Served hot! Think british breakfast blend. That's exactly what this is like. It's just not bitey like the classic twinnings one.

Are these the sealed or stapled tea bags?

No the 80 box are two joined bags made for a pot of tea. If you want single cup tea bags with the staple in order the 100 bag box.

How many mg of caffeine is in this tea?

A bag of Yorkshire Tea contains 3.125 g of tea. If the 3.062g caffeine per 100 g of leaf is correct, then one bag has a total of 96 mg of caffeine. Note that you would get this full dose only by consuming the contents of the bag. Most brewed infusions aren't 100% efficient at extracting caffeine.