Pet WQ's still exist, although they are not so important this time
What you should think about on your main?
1. Decide which starting covenant, which covenant you may change to, and when
Choosing a starting covenant is difficult in itself, consult your RL. It is likely, you will have to change the covenant for mythic progress if you change specs (for example, a mage from frost to fire) or need a specific covenant on the boss. Better prepare for this in advance.
2. Decide on the order of crafting and upgrading legendaries
Most likely you will need several different Legendaries for different bosses (including multi-spec). Decide in advance in which order you will craft legendaries (see the section on legendaries).
3. Plan spec for leveling, LFG, pick up gear and trinkets
It is desirable to have a universal mobile spec. You will not change gear until lvl 60, especially Azerites, neck and cloak.
4. Prepare tank and heal specs for your class
Use 2 gems from BFA addon to increase your running speed. Both gems together will increase your speed by 8%.
5. Prepare professions
See the professions guide.
In the Shadowlands, it is quite easy to maintain a few alts at a decent level - no need to farm Azerite or similar. That's why you should make a lot of alts (2-3 alts) I don't really understand the perspective of doing heroic raids splits because of the removal of seals. On heroic week without seals there wont be a lot to trade, unless, of course, you invite friends like Limit and Echo do. And on the mythic week 213 ilvl loot (heroic raid) will be available in keys and you will be able to loot it without splits (210 ilvl in keys before that).
There are no unique items other than trinkets in the raid (there are no Azerites or sets). But since the alts are not difficult to make, it is better to make them right away, they will be useful in progress for the class stacking and splitting the 2 last bosses on mythic weeks (increased 220 ilvl from the last 2 bosses).
On alts, it is also better to decide in advance on the covenants, clean the bags and the quest log, prepare the professions