Tick anything you already have, in any order. Quests unlock once this is done.
The test kit is the one people skip and the one that keeps fish alive. A tank kit bundles the filter, heater and hood for less than buying them apart.
2 things left above. Quests are real things you go and do, so they only make sense once you have what you need.
First one waiting: Pick a tank and set it up level and rinsed