You've been given very good advice re: red caps and Penn in general. Just to emphasize, Penn coming in from 7th Ave. is very confusing and can be overwhelming even for those familiar with it. Give yourself a little extra time to get through it to the Amtrak/Club Acela area if you choose to enter on 7th (entering on 8th a little less intuitive but less overwhelming).
In DC you won't need a red cap as you'll board directly from Club Acela. It has its own door out to the tracks and they board from the club before the regular boarding call. The tracks are literally right there (unlike at Penn).
In Boston it's similar to Penn but the station is less confusing and overwhelming. Often there are red caps right outside the lounge and you can just tell them you'll need help getting onto XXXX train. They will then come into the lounge and get you when it's time.