Book of ACKSalted Deeds II: Design Decisions

Having laid out the intended structure of my religion revision, I now find myself at the tricky bit - implementation.  I have a few concerns that I definitely need to keep in mind throughout this process.

• How difficult should it be to work minor miracles?  And at what cost should they usually come?  On the high end, what can a character with an 18 Piety and a bunch of vows make happen, and how often?  On the low end, can a character with 3 Piety even have a chance of successful prayer without vows?  Does prayer's efficacy or scope scale with level?  What should the probability distribution on success look like?  
• 2d6, reaction roll style?  Problem: small modifiers rapidly dominate the die-randomness.
• Or d20xd6, RL&L-table style?  Problem: need lots of table entries, d20 split into groups of 5 is not very granular and is also dominated by die-randomness.  That might be desirable for pentulant Classical-type deities, though.  What goes on the d6 edge of things, though?
• Something else, like 2d10?  Gives a bit more modifier-space than 2d6, without the extreme swinginess of a d20.  Strongly tends to the mean, though.  d12+d8 flattens the middle range, but doesn't change much beyond that.  I dunno man, coming up with good probability distributions is hard when you're not exactly sure what you're looking for.
• Prayer Spam, particularly as it interacts with henchmen and domains.  If you're the guy with 3 Piety, but you have a henchman with 18 Piety, can you get him to pray in your stead?  What about at 14th level, when he's basically the pope?  Should prayer frequency be a per-player resource, as it is assumed that henchman prayers are ultimately for the player's benefit?
• How does the Divine Power subsystem interact with the new system?  What about item creation?
• Divine power can be burned to provide a bonus to prayer rolls, or just to increase the scope of the results?  I actually sort of like the idea that divine power is the only significant way to scale up miracles - it makes conversion / expansion and temple-building a priority for anyone planning to make regular use of prayer.  Also provides an explanation for heresies and rivalries within a church - priests compete with each other for influence over the flock, and heresies tend to bring the doctrine closer in-line with what the flock wants to believe in order to win them over.
• And as long as you keep your vows, heresy's A-OK in the deity's book.
• Divine item creation is superseded by receiving magic items as gifts from deity as a result of high prayer roll?  (Athena's shield, Hades' helm, and Hermes' shoes, Nethack granting spellbooks on prayer, ...)
• Sacrifice quantities.  I desire to make sacrifice difficult to game, in that a major / high-effectiveness sacrifice should actually cost the PC something fairly dear.  Fortunately, deities know things and can avoid accepting gamed sacrifices, but it's a hard thing to nail down and provide guidelines to players.  Maybe use the Standards of Living table and the bribery rules as a starting point?