SoP Staff, caster, and feat talent stacking

Question

This is a rather cheesy question about min-maxing.

Staffs in SoP work a little differently than plain Pathfinder ones. The enhancement bonus applies to CL of the sphere effect, and extra talents can be included in place of +1 bonus, much like how weapons and armor and their enchantments work.

Greater Blast

The damage of your destructive blast increases by one die. You may take this talent an additional time at 5th caster level and every 5 caster levels thereafter; the effects stack.

Staffs

Any caster wielding the staff gains access to a magic talent contained within the staff. If this talent is a (form) Conjuration talent, it may be applied to any companion the caster summons, but no more than one creature at any given time. To contain an advanced talent, a staff needs a minimum caster level equal to that talent’s prerequisite caster level, and must contain all of that talent’s prerequisite talents. A staff may gain this special quality multiple times.

Circle Casting

You may aid another spellcaster who also possesses this feat, granting them a temporary +1 bonus to their caster level, as well as granting them access to your spell points and talents as if they possessed them. You must spend a standard action every round to maintain this ability, and you must be within 30 ft of the caster you are aiding in this manner.

A target may be aided by multiple casters at once in this manner, but all involved casters must remain within 30 ft of each other, and the effects are not strictly cumulative. It takes one aiding caster to add a +1 enhancement bonus, three to add a +2 bonus, six to add a +3 bonus, ten to add a +4 bonus, and fifteen to add a +5 bonus. No caster may receive more than a +5 bonus in this manner.

So if you had a +1 staff with greater blast (1) and a caster who had taken greater blast once, they should be dealing damage at 1d10 per die as the talents should stack. Two casters with circle casting should also stack due to this?

Answer 1

While you're misinterpreting the effect of greater blast (as mentioned in Derfael Oliveira's answer, the talent increases the number of dice you roll, not the size of each die), you're correct that multiple instances of greater blast from separate sources will stack. However, the rules are unclear with regard to greater blast's caster level limitation.

You may take this talent an additional time at 5th caster level and every 5 caster levels thereafter...

If interpreted as a caster level prerequisite (which appears to be the most likely interpretation, though SoP's rules are quite vague on the subject due to prerequisites being so rare in the system), this requirement would presumably extend to additional talents obtained from staves, circle casters, and other external sources. In other words, no matter how many copies of greater blast you're getting from staves or circle casters, your blasts can still only get one extra die, plus one for every five caster levels (calculated after adding your CL bonuses from the staff, circle casting, or any other sources).

On a side note, it's never worth it to add greater blast to a staff, even if your DM allows staff-granted greater blast to bypass the normal caster level requirement. "Magic Talent" is a +2-equivalent staff enhancement, so for the same investment, you could get two extra caster levels in the destruction sphere (which would give you the same +1d6 damage as greater blast, plus an additional d6 if you spend a spell point on increased damage, as well as +1 to save DCs).

Answer 2

The Greater Blast talent does not increase damage die size, but rather the number of damage dice. For example, a destructive blast that would normally deal 3d6 would instead deal 4d6 with a single Greater Blast talent.