How could it take any less than eternity for us to enjoy an an infinite God! You considered only finite activities; God is infinite. Infinitely good, infinitely beautiful, infinitely wise, infinitely holy. There will be grace afresh each day, for eternity – a new reason to praise God each day.
There needent be any more than one activity, though I am sure there will be, for that one activity is itself eternal.
Bring on the sweet blissful fullness!
 

It’s forever, and ever, and ever. Never-ending, ever. All you will be doing is singing praises or whatever.
The other problem with an eternity of existence, is that you will run out of things to do. Even if you do every single activity in existence, every single POSSIBLE activity, in every possible way, wearing every possible set of clothing, with every possible combination of every possible person… You will get bored. Because you’re there INFINITELY. Forever. No matter what you do, no matter how long your activity takes, you’ll finish it. Then there’s the next one, and the next, and the next. You’ll do everything so many times over and still have an infinite amount of time left to do things in. Even if you waste and infinite number of years doing infinitely many things, it’s the nature of infinity that you’ll still have an infinite number of years you have to fill up.
Bring on the sweet blissful nothingness.