to answer the first question - 3 weeks, 6 weeks, 9 weeks, 3 months, 6 months are the biggies. after that it seems to depend on the baby. so it probably is likely that he's going through a growth spurt now.
you will probaby just be a little off for a week or so (sometimes 2) what may end up happening is something more like EAESY for a bit. the one thing you want to keep an eye on is that you do not feed him to sleep and risk introducing that prop.
HTH