My experience is mostly from the reverse commute to yours. Here’s what I can share.

There isnt always an Acella and sometimes you need to switch from a Metro North train to an Amtrac train in NyC, which means leaving Grand Central and traveling across midtown to Penn station mid-journey.

Also, you cant arrive back to Philly from Stamford by train before 10:30am should you ever wish to.

Traveling business class on Acella costs more but you get to pick a seat. Non-business class is no reserved seat. Sometimes I have trouble finding one or finding two together etc.