ERC makes a great bow but can be finicky. For a 28" draw I'd go no less than 66", 1 1/2" to 1 3/4" wide out half each limb then taper to 1/2" tips for now. I'd also rawhide back it.
When you cut the tree cut it long, 6' at least and seal the ends. After a week or so split the log in half and set it off the ground and out of the wind and weather to season. After a month or so you could split it down to staves.