Let me start off by saying that this whole paperwork thing is WAY over-blown on these internet gun forums.
But, yes. If you are planning on buying several NFA items, it would make matters easier and quicker to do them all at once. Simply because you are getting it all done at once, and you only have to endure the waiting process once.
This brings up another thing I learned along the way. If you have a local dealer who stocks inventory of suppressors, you should seriously consider buying one that he has in stock. Even if it is more expensive than one you could order. Even if it isn't exactly the one you had your heart set on. If you have to order a suppressor from the manufacturer, the wait times are very long. And there is more paperwork that has a good chance (based on my experience) of getting screwed up. Ordering a suppressor increases the steps involved, the paperwork involved, the wait times involved, and greatly increases the chance of some foul up in the process. When I bought my NFA stuff, the wait time with the ATF was the easy part. Waiting to actually get the stuff to my dealer was far longer. And in EVERY SINGLE CASE, something got screwed up in the process. Paperwork got lost, in one case they sent the item to the wrong dealer in a completely different state and that dealer didn't know what it was so he just put it in his safe and didn't tell anyone about it, in one case the actual owner (FFL holder) was out of the country on vacation for a long time........................ By far, the easiest transactions I ever did were when I bought something that was sitting in the dealers display case. Unfortunately not many dealers stock very many NFA items.
Not to discourage you, but a couple of my NFA purchases took over a YEAR to complete. And it wasn't because of the ATF, it was because of the dealers and the manufactures.
Basically, no body cares about this but you, so nobody is in a hurry, they leave paperwork sitting for weeks that could have been taken care of, but wasn't. Losing paperwork. Not calling you to tell you the stuff came in.............................. When you start this process, you need to be on top of it at all times. Again, the sign-off isn't a big issue. The ATF isn't a big issue. The dealers and manufacturers involved ARE a big issue and you have to keep on them and keep them moving. You lose a week here, you lose a week there. They don't care, but you do.
You know the rest. In the books you have read
How the British Regulars fired and fled,
How the farmers gave them ball for ball,
From behind each fence and farmyard wall,
Chasing the redcoats down the lane,
Then crossing the fields to emerge again
Under the trees at the turn of the road,
And only pausing to fire and load.