From the Escalation V6 rules, page 197, under Two Weapon Fighting.
You fight as normal, generally using the
weapon in your main hand to attack. If your
attack roll is a natural 2, you can reroll the attack
but must use the reroll. If it suits the story of
how your character fights, go ahead and use
your off-hand weapon for this rerolled attack,
but you don’t have to do that unless you want
to.
The Fighter has the Power "Two Weapon Pressure" as well. However, the Ranger is to go-to guy for dual wielding.
The advantage for two weapon fighting as a Fighter is that you have a 1 in 20 chance of re-rolling an attack, plus on a miss, you get a +2 attack against the same target next round (if you pick Two Weapon Pressure). The downside is you lose AC from not having a shield. (Two Weapon Pressure is a level 1 Power, and it triggers on any miss, so maybe it's good enough to compensate for a lack of shield)
The question will be a real issue in case of multi-classing, since Combat Boon is a Cleric's power, while only Fighters and Bards have flexible attacks.
My conclusion is:
Flexible attacks are not basic melee attack
Hence, you can't use Combat Boon with Flexible attacks, but I would rule Hammer of Faith as "yes" because it is a passive buff, and because it's a Daily. The game goes out of the way to make Daily powerful (transparent targeting being the first thing I can think of).
My reasoning is base on the text for hampered, page 172 of the rule-book.
You can only make basic attacks, no frills...(Fighters and bards, that
also means no flexible attacks) [Emphasis mine].
Also, additional attacks per turn granted by powers or talents (the Fighter's Counter Attack, for instance) cannot be used as triggers for flexible attacks. This reinforces that the two (basic attack, and flexible attack) are two different beasts.
Hence, I guess the intent of the rules is for flexible attacks to be considered as powers with a chance of triggering depending on the dice roll. Essentially, I guess my stance is "only one effect from one attack" - which I would argue it's the rules' intent because you can only trigger one flexible attack per trigger, despite being eligible for more than one.
Best Answer
13th Age SRD is sufficient to enjoy benefits of Archmage Engine.
You will be missing out however. For example:
Rob Heinsoo and Jonathan Tweet's writing. In the introduction they promise to provide a product of their long dalliance with RPG games. Rules are provided in friendly informal and entertaining way: "We aren’t telling you exactly what..." to do, but you will get default option and hints/advice on variants.
Core setting and icons. They are presented in a way to give you room for interpretation and to grant you opportunities to do stuff. While a bit irksome to old school fans like me (I do love hard facts), the players are likely to enjoy being the center of attention, and the world just waiting to follow-up with crazy shenanigans.
Speaking of icons, without core book, they are unlikely to be useful. Consider skipping icon rules until you get the core book.
13th True Ways provides very advanced classes and complicated monsters. Bestiary was probably the most awesome book of monsters until Bestiary 2 was released.
The list would not be complete without mentioning living dungeons and Eyes of the Stone Thief. Living dungeon is a malignant entity that thrives on obtaining new buildings (rooms), and treasures, and creatures. Stone Thief is a Moby-Dick of living dungeons. And Eyes of the Stone Thief is probably the most incredible campaign built around hunt for an elusive predator that ate your home town!
That said it is strongly advisable to review/obtain the following free stuff:
13th Age SRD PDF (obtainable from DriveThruRPG) is the most up-to-date and complete version SRD. It also contains quite a few very important rule update and clarifications. I consider this a mandatory version of the rules.
Form fillable PDF of character sheet. Printer friendly.
Master list of online resources. Make sure that your players read one-pager summary of the system, while you, a GM, keep two-page system core at your fingertips.