1. Miles expire. I can't remember off the top of my head how long they stay valid for, but I think it's 3 yrs. Your account will show well ahead of time how many miles are due to expire and when.

2. 25k miles in a membership year gives you Silver, 50k gives you gold.

3. Silver is only good for the 25% bonus on destination miles. Gold gives you all Silver benefits as well as Star Alliance Gold benefits, including priority check-in, lounge access, 20kg extra luggage, etc.

4. There is a pdf chart you can download from the KrisFlyer site. It shows how many miles are needed between various countries.

One of the reasons why you might not have been able to upgrade (apart from lack of miles - though you can also purchase those online) is that you need to purchase a ticket on a "flexi" fare. Tickets bought in saver tariffs do not qualify for upgrades.

5. Only miles earned by yourself will be credited to your KrisFlyer account. Other people must have their own KF account to have the miles they earn credited. There are no joint or family accounts available.

You can of course spend your miles on someone else, be it for tickets or upgrades.

6. If you are Gold and flying on any Star Alliance carrier (in any class of travel, even economy), then you have access to the lounge. You can also bring in one person with you as long as they are also flying on a Star Alliance flight that day.

7. Miles don't expire after one year. It's just that miles earned from flying also count as status miles, and it's status miles that are reset each membership year. So yes, you need 25k for Silver or 50k for Gold in one year. This is just for status. But overall miles are valid for a couple of years and can be accumulated over a decent period of time.