The only thing that made me feel worse than choosing warlocks in BFA was trying to maintain multiple teams for rep and gold. I would definitely recommend devoting your time to 1 team. Personally I would shoot for a team that can easily handle most of the content the game offers. A highly mobile, versatile team with a deep toolkit that offers a lot of team synergy and allows you to grow as a multiboxer.

My original crew was BDK / RSHM / 3 * Warlock but I suffered enormously trying to get them to do anything M+ because they are immobile turrets and BFA is a movement heavy experience. The next problem was that BFA is extraordinarily unfriendly to alts. So if I wanted to switch mid expansion I'd have to regrind everything. That wasn't happening.

Anyway tl;dr: they are nerfing some of the alt unfriendly stuff by making essences available to alts and rewarding corruption gear more frequently. So for the next few months playing alts might be worthwhile but for you I'd just stick to 5 that have a lot of freedom. Do NOT make the same mistake I made by picking with your heart and not with your head.