I add peppers to the secondary just by themselves and sometimes to the keg in a tea ball or hop bag. It may be best to start with just one chipotle in 5 gallons and check it in a couple days for heat and flavor. If it is not intense enough you can add more, but it is very difficult to go the other way.
By the way a smoked porter is perfect for pepper additions. What kind of smoke? What style of Porter?
I do a vanilla porter with mulatto chilies. The local spice shop owner (Savory Spice here in Boulder) works with brewery’s like Avery’s, Left Hand, and Oskar Blues. The guy knows his stuff! He suggested to me just to cut them open on one side to get more flavor and then throw them in right after the boil to disinfect. It’s worked great for me!
To give a guide, the mulatto chilies are what he called “a 1 or 2 out of 10” on the hot scale and I find that 2-3 give just enough to where it’s not too spicy that it overwhelms.
You might experiment with the canned chipotles in adobo sauce. They are already hydrated by marinating in the adobo. Very smoky and probably just as intense (maybe more) than the dried. I prefer these to the dried chipotles for cooking needs. I like the San Marcos brand.
Cuidado! They can be quite fiery! One or two at the end of boil then add to secondary if the heat/flavor isn’t right.