>>96534562
Hobbying wise, knights can be a bit daunting for a first army, I would strongly recommend you watch a good amount of videos on painting them to give you an idea of how to tackle painting them. Going for drybrushing and or airbrushing is recommended for building up your colors quickly without layering your paint too thick (airbrushing is a whole separate item that requires setup and practice to properly utilize as well so be aware, regular brush skills are always relevant). That being said Chaos knights are absolutely a great looking army and its a fucking shame how rarely I actually see them fully painted.

Gameplay wise, The issue with knights is that they are by nature a skew army. By that I mean any game you take knights into typically go two ways:

1: Your opponent does not have enough Anti tank and you steamroll them
2: Your opponent has a lot of anti tank or anti knight options and you loose knights quickly

That is generally speaking, a skilled player will still win against knights without a lot of anti tanking by playing objectives/secondaries correctly but that's something you won't have to deal with for a while. You need to also consider that as you generally have fewer units than your opponent, learning how to best utilize each of your knights for movement, target acquisition and board control are essential.You CAN offset the skew issue somewhat by running some armigers/wardogs, and a benefit of chaos knights you can ally in some daemons which a lot of people do. Be aware some players get pissy about playing against knights.

All that being said take your time research the models, watch hobbying videos on your faction, read lore and come up with paint ideas. The more research you do in a first faction can help ensure that you find something that you'll truly enjoy. Always remember, what is good and bad in terms of gameplay is temporary but those models on your shelf are there forever for you to look at enjoy and be proud of.