Here is something else that you might figure into the mix. With the possibility of the hemlock going bad, have a second plan in place in case it does. Find out size and type your using. Put them on centers in such a way that if the hemlock fails, you could tear the hemlock off and put more new joist in between what is already there and you would be good to go with a solid deck. Just leave a bit for wiggle room to get them in, make sense?
Time for you to get to work, be safe......
