Two certainly works well, as an initial test.
Start with one, and RAF invite yourself.

That gets you RAF on both accounts, assuming you level toons together who are fairly close in levels.
Call the first account A, and the newer one B.

If you decide to move up to five.
You can have RAF on all of the accounts quite easily.
Most likely, your best booster will be an existing toon on the first account.
But between A/B, whichever one has the best booster will be the account in the three link chain:

A > C > D
B > E
With "A" boosting BCDE.
C/D and B/E, each have an RAF link... or toon of about the same level that they're grouped with, while "A" boosts them.
And because A is part of the A/C/D chain, they'll receive granted levels, the free month, the RAF mount, etc...
You could do this secondary RAF stuff, months later; all five accounts will have RAF, starting with two.