I’m not sure about claiming the 2nd chest: once you have enough points the area with the “price” should turn into a button. You can also see from the indicator at the bottom that you have reached the goal.
For tips: ask yourself how much you want to spend on this, and how. If you regularly spend $100+ in a weekend of play, just keep on doing what you do, you’re 70% there and you know the way. Good for you!
If you don’t and you’re planning to spend a bit extra just for the event, please note that the only good reward is the last one, so a commitment of $140, and about 3X the points for the random ST chests. Also, spending extra to get the 3rd or 4th chest can end up in you gaining a Geb wand + ring.
If you still want to proceed with this, I’d look at the packages and decide what you need the most: pet food, vaults, or char slots.
Too bad there are no skins for sale any more!