I used Winsor and Newton paints to get the colours, if you're still interested then here are the links. Unfortunately I kind of eyeballed it.
This is the blue (mixed with some black and white) https://www.amazon.co.uk/gp/product/B0060KTTO2/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
The cream (or titanium as they call it) https://www.amazon.co.uk/gp/product/B0060KVWI8/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
If you're interested in seeing what other models look like I have a few done so can send them over if you want?
I recently started a CSM army and had kinda the same dilemma. Firstly I'd say that the Start Collecting box is good value, and you get a bunch of models that you can't get anywhere else (Venomcrawler, Obliterators and Greater Possessed). It would be a good core for your army, but doesn't really take advantage of your main strength of World Eaters, which is being able to take Berzerkers as troops. So you'd still want to supplement that with a few boxes of Berzerkers.
But I also liked the look of the Vengeance Warband set (Terminator Lord, CSM, Terminators, Havocs and a Rhino) I asked at my local store why this seemed to be sold-out everywhere and when they'd get new stock in, and he explained that around Christmas time they release these sortof alternative starter sets for a short production run so they weren't available anymore. Which is to say that in a month or two there's likely to be another similar set being released which might suit your purposes.
I'd also say that the berzerker kit is looking a little dated at this point, which is why so many people like to kit-bash it with the AoS khorne kits. GW have said they're looking to do a few new releases for each faction in 9th, and I believe them and the bikers are the oldest models on the Chaos roster. So perhaps you could gamble that they'll be updated in the relatively near future, but as it's not been mentioned specifically up to this point Chaos is unlikely to get any love this year.
So if you want to get cracking, I might say start working on getting some berzerkers together (whether that's a regular box or a kit-bash) and by the time they're done you might have a good deal on a Christmas army box to fill out your other specialist slots.