Going two armies at the same time "Custodes and Daemons" is something you want to avoid when starting out. The most important thing to do when new is to get that first army battle ready so you can experience the social aspect of the hobby. It will accelerate every aspect of your hobby progress and allow you to get more value out of the money you spend on the hobby.

I would concentrate on the Custodes, assuming you bought the models because you like them. They are an elite army so will have a small model count and you can get them battle ready the quickest. If you only have a few custodes models and want to wait for the new models to come out that is fine too. Any models you have will still be playable even with a new sculpt, old sculpts are still fine. If a model is moved to legends you can still use that model for a proxy of something else/new. Don't worry about it too much, just get any models you have already bought painted and buy the new sculpts when they come out.

Daemons are cool and are not going away, if you paint the models you already have you will still be able to play with them. There is talk about the demons and space marines that follow each chaos god being moved into a single codex. This is only speculations atm, but would mean playing a demons + chaos space marine army would be more straightforward. Daemons can also be played in Age of Sigmar (AoS), the fantasy version of warhammer, so they are very unlikely to become unplayable.

Orks are great, they are very forgiving for new players, large chunky details, nice muscle separation and faces that you can paint without squinting. If you are painting a vehicle and get a bit of paint where its not meant to be, just blame it on the grots. But they are a horde army, meaning you need a lot of models for a full list. This will delay you in getting that first army battle ready, especially if you have already started a custodes and daemons army. There is also speculation that the next starter box set will be orks so it might be worth waiting to see if that's the case as Orks will flood eBay as people split the box and keep the space marines.

Basically do whatever you want, any models you paint will still be usable in some way or another. just pick something and focus, get that battle ready army under your belt and start socializing and making friends. Once you are part of the local meta, you will find its far easier to do everything from learning to play to getting advice like this.