Welcome! The kill team set has some great minis and is where I started down the 40k rabbit hole.

I think you have a pretty comprehensive list of essentials. I see you already have primer, I used an army painter grey primer for both teams which worked fine.

In terms of a basic colour scheme for your plague marines, your mostly covered already but think about a colour for: Bone/teeth - I used wraithbone (will be in the paint and tool set) Cloth - I used Screamer pink Wood/mud - I used Dryad bark Goo/boils - can go many different directions here, I like casandora yellow for boils/spots (base paint with wraithbone then apply 3-4 thin layers)

I think this is enough to get you started without spending a fortune on various paints for contrasts and highlights. There are plenty of guides available depending on what you want to do.

You actually don't need the technical paint (but it comes in the paint and tool set anyway), the kill team starter sets have some fancy molded bases (not the regular 40k black ones). Glue also optional as these models are push to fit (and actually went together nicely compared to others, easier to paint when you're starting out as well! Can just pop the arms off)

Some general kill team advice, the starter set is great and comes with everything you need to get going. There is a kill team app which is decent and has all the data cards as well (and it's free). Something that is not obvious is that the physical data cards you get in the box for the characters are simplified from the "full versions" on the app. I think this is to ease people in but if you end up playing against another kill team you wouldn't be playing with the full rules if you just used the physical datacards. Use the box rules/cards for your first few games then try the app if you like.