Am I more likely to mint if the coins are older? I thought that older coins just means you get more from minting them? Am I more likely to get a successful mint block if I'm using "more" coins? What are "more" coins?
You chances of minting are dependent on the “coin age” of mature coins available in an address you control. Coins are mature when they’ve sat static in an address for more than 30 days. Between Day 30 and Day 90, the chances you’ll solve a block increase as your coin age increases. After Day 90, you’ll stop getting gaining an advantage, but you’ll continue to attempt to solve the current block as if you are perpetually at Day 90. The reward for solving a block, when you do, will be calculated using the “real” coin age (Day 1 until whatever day it is when you solve it).
The stake’s coin days are calculated based on the number of coins used, so someone who attempts to use 1 PPC to solve a stake will have at maximum 90 coin days, where someone who uses a stake of 1000 PPC will have 90000 coin days. However, one thing to consider is that it’s still not a “sure thing” for the person who has more coin days at stake to win. For example, right now, I’m attempting to mint with a stake that is larger than most of the recent ones that solved PoS blocks (well, not 97689, that was a lot larger than mine!).
Does my client aggregate all the coins that came in at all its addresses when it mints? Or just the coins sitting in one address? If so, is it more advantageous to me for internally transfer all my coins to one address?
From what I’ve seen in the code, and from what I’ve read on the subject, each address is treated individually by your client. I asked Sunny King for clarification on the matter of whether or not the client is concurrently trying to solve blocks with any addresses that have inputs that meet the requirements for maturity, or if it picks the address that has the highest matured coin age and uses that exclusively. I’ll share the answer with the community once I hear back.
Consolidation into a single address could give you an advantage, but there are other factors to consider (security, anonymity) that may outweigh the benefit. That’s a decision you’ll need to make, but remember that if you move your coins into a single address, that the transaction used to do that will reset those coins’ coin age back to zero (just like any outgoing transaction would).
I see there's a "difficulty" with PoS. How is the diff calculated? Similarly to PoW, in that it's based on how many people are PoS minting?
This is a question that I asked Sunny King, too, because I don’t quite understand what it means. I understand how the difficulty works (it’s used to ensure consistent block spacing), but what I’m not quite sure about is if it’s related to the number of concurrent people attempting to mint, ala the PoW difficulty, or if there’s another mechanism that calculates it. Sigmike, ppcman, alertness, fuzzybear or others in the community who have more experience with the code may be able to better articulate how this works.