By 9 months you don't need to worry about the 4 hours, its more like 4+ hours. You let your guy have the 3.5 hours A time, (or more, some babies manage more at 9 months- up to your baby though), and then let him sleep for up to 2 hours (some people cap the nap at 2 hours, i actually let my guy sleep- but that's up to you) and then feed him. At 9 months he;s probably having at least one solid meal- if not 3 solid meals, so that, and the ability to have more milk means he can manage it.
There is no 'ideal' schedule- but usually by 9 months babies are on 2 naps- my guy does a long morning nap at about 3.5 hours A time and then a short afternoon nap. But sometimes he does 2 2hour naps, other babies do a short AM nap and a longer PM nap- They usually need between 1-2 hours at least once a day for their sleep to be restorative at 9 months.
Please let me know if you have any other questions on your EASY routine!!