I'd still go Kael as that'll be your best campaign farmer. 

Then I'd immediately go with Venus and would be happy putting legendary books into her as you get them since you're going to use her in pretty much every piece of content for a long time, and she's going to be your defense down option. Plus, she brings weaken to go with that defense down plus the poisons and HP burn. Great pull. 

Venus being this good, is it still better to go kael first? And Kael > Ronda? Like they are both aoe dmg fast clear no?

In a sense, yes. Kael will be easier to book out - and thus get full value from - and is better in the most important earlier game content: Dragon and CB.

Then Venus can be our debuffer, defense down that will go before Kael in whatever we're running them in. But first we need the campaign farmer built up to 60, masteries and all so we can farm efficiently. 

Thx man!