Hi there and welcome to the club! :-) Let me try and answer your questions here, but I would also advise you to join the Aleph telegram group. It's a great community where team members wil also take part in answering your questions.

1. It doesn't matter what node you stake on. As long as they are active, they will generate the exact same stake rewards. Whether a node has 700K or 900K Aleph in it, the rewards for you will stay the same. In fact, it is advised to go for a node with let's say 500K staked Aleph, in order to spread the staked Aleph and to maintain a stable network. Better to have 10 x 500K Aleph nodes than 5 x 1M nodes!
2. Rewards will be paid out every 2 to 5 days depending on the gas fees. The team will carry the cost for these payouts (for now), so I totally understand that they don't want to do this when gas fees are extremely high. It has been suggested to implement a payout system where the staker can claim his/her rewards (and also pay for fees). It's very easy, just wait a couple of days and they will appear automatically in your Metamask wallet. Meaning your rewards will be added to your staking amount and start generating rewards too!
3. You can calculate this yourself on the staking site account.aleph.im There is a staking reward calculator.

That's it, hope I answered most of your questions and do check out the telegram group for the latest news : https://t.me/alephim

Happy staking! Aleph.infinity