I'm no FFL dealer and don't claim to know what all the Feds are wanting now, seems to change every other day!
I do know that here in Iowa I can buy ALL the long guns I want at one time without any permits. The dealer has to do the phone check thing if you don't have a permit to purchase handguns or a CCW permit. If you have either of those permits, they don't even do a phone check.
I can also buy ALL the handguns I want at one time if I have the state, handgun purchase permit, (which you need for ANY retail handgun purchase) or the higher state CCW permit.
If I buy more than one handgun in five days, my FFL dealer has to inform the Feds about it. I do this all the time, just did it last month, bought 3 new handguns in one day. I've bought 9 stripped AR-15 lowers, (the only ser# part) at a time before without any problems. Thats the same as buying 9 rifles at the same time.
Like JonM said, some states even have a "1 gun a month" policy. If you comply with your state laws, you should be GTG on the federal end of it.
I've never had the BATFE contact me about my purchases.