First. I see no time duration on the property.
Is there anything preventing you from boosting and then going exploring or whatever? Basically to always have it ready for the first turn of combat, there is no sustain or anything like that on the ability.
As far as I can see, there is no duration. The GM should probably put in some sanity duration limits such as, 'until your next daily preparations', but even that is not technically necessary.
The limitation is that you can only Boost the weapon once - multiple Boost actions don't stack.
The other one that I think changed between playtest and release is that Boost no longer requires Expend of ammunition. At least, not as far as I have found.
Second. How does it interact with Area of Effect Attacks.
Does it affect a single target within them? or All of them? Something else?
By default Boost isn't on any area effect weapons, however the soldier can turn any 2-handed weapon into an area effect weapon with Whirling Swipe.
Correction: Whirling Swipe only works with Melee weapons.
Requirements You’re wielding a two-handed melee weapon.
The Melee weapon gains the Area (Burst 5 feet) trait and that is why it mentions using Area Fire with the weapon.
That said, from what I see if a weapon had Boost and could be used to attack multiple targets with the same attack activity (a ranged weapon with Boost and Automatic traits, or a 2-hand melee weapon with Boost and using Whirling Swipe), then the damage boost would apply to all affected targets.
Yes, it lasts forever and it doesn't cost expend anymore. Presumably this is how ranged weapons got buffed for low level use, because certainly nothing else meaningful happened.
It's really only a benefit for (1) round 1, (2) if you actually hit. If you're a caster who hasn't picked up martial weapons you're restricted to the short ranged Sonic Rifle and can't use spell gems, healing actions/consumables, etc with a free hand. If you invest in Weapon Training general feat and the Boom Pistol you get the same damage increase (8 avg vs 4.5 avg on a laser rifle) on that round 1 hit and keep the hand open.
The Plasma Caster, if you can spare both hands, is a better option for a bit more range and damage (10 avg boosted vs 4.5 on all non-advanced "semiauto" options) for Envoys who want to use 1 action directives a lot (great when you can get that early feat chain to make someone your Mark for 2a->1a Get 'Em and 14 avg on their one full MAP strike every round) or Operatives who want to usually strike once (2a Aim/Strike+ feat, 1a Boost) but don't like snipers and want the flexibility to strike twice or break up their actions more.
The painglaive is a melee Boost 1d10 weapon.
Whirling Swipe is definitely going to work with it.
I think this is fine because boost + swipe costs 3 actions and you need precise positioning to capitalise from it. So you need to
a. start your turn surrounded by enemies (which, TBF, it's what the soldier class is designed to do), or
b. boost on your previous round, so that you can stride in position and swipe, or
c. be hasted so that you can stride -> boost -> swipe.
It's still an insanely powerful combo (which completely eclipses the Doshko also due to its lack of reach), mind you.
Note that if you Boost and area fire as a Soldier, your Boost damage will go to the Strike against your Primary Target, unless you decide not to do the Primary Target at all - which is a big tradeoff.
Also, I just noticed this combo:
Level 2 Soldier (Close Quarters) with Painglave and Shot on the Run.
For 3 actions, boost your painglave, stride, and strike. You only get a 5ft burst and not the 10ft that you would get with Whirling Swipe though.