Lots of good advise, but I will add some of mine.
My wife and I have been riding tandems for over 30 years.
When she was younger and stronger we rode single bikes more and she kept up pretty good.
Now that she is 60 and we both work full time it has been more difficult for her to maintain fitness.
She has a nice road bike but rarely rides it as I am much stronger than her so I have to ride very slow and we can't do many hills or longer distance.
The tandem is the great equalizer and removes the element of difference in ability. We can do rides that are hillier and longer and more interesting that otherwise would not be possible. As others have already said, as captain you have to put your stokers needs and comfort first. I have learned this the hard way and have had to adjust my way of thinking of riding competitively versus riding for enjoyment. We have owned three tandems, each one nicer than the last. The one we have now is about as good as it gets and will probably be our last. It costs what you might pay for a nice used car but is clearly one of the best investments I have made. With your size you are going to need a larger size tandem. I would keep looking, Santana, Cannondale, Burley, Comotion are all ones to look for. An older tandem is probably going to be quite heavy but will serve your purpose especially if you are riding on flatter roads. It may also need some working on so it would be good if you know how to work on bikes or know someone who does and you can always get good advise here.