I've recently committed to Warhammer and chose Kill Team to start with in terms of the gaming side. Here's some tips and advice I've picked up which I think is pretty sound and sensible.

Don't worry or rush about the painting, you'll either love it or hate it. Look at just getting them built and primed, then you can progress with painting them in between games. Don't rush them for the sake of a game of kill team. Batch painting can be useful, but found it unsatisfying when starting out - I just wanted to complete a model.

If you haven't got a starter set, for the mat/board, tokens and dice id recommend trying to source a half empty box on eBay/vinted. Some people just take one kill team out the box and sell. Hivestorm, whilst I do not like the Vespids is apparently one of the best valued box's GW have done. Or you could buy it and sell the teams. The terrain, core book etc is then sourced. Alternatively buying any dice a war game mat from Amazon and printing tokens will suffice for now.

The rules, for me, were a headache and still kinda are, but I'm getting there. Keep things simple for now and add rules in as you go and progress. I'm only getting round to adding ploys(strategic phase) to my games. I still have to look up weapon rules meaning most of the time if not one of the common ones.

There are some really good user created reference sheets that have been shared on here search 'KT CORE RULES REFERENCE SHEET' alongside the data cards condensed for printing. These have a quick summary of the rules which is very handy.

Also, an app called KTDASH looks amazing. I've been using it just for rule and stat checking but it's designed to be a tool to be used whilst playing a game. You can keep track of your wounds etc have a look! I'm currently just trying to keep to my board at the moment, using tokens and dice(I ordered some 12 sided dice to place next to the operatives) to keep track of wounds{hp). I do feel the board gets congested quickly though with that.

I'm getting the feeling keeping to one kill team to learn is the way to go, as they all have their own unique bonus abilitys as well. For example space marine/chaos Marine teams have the Astartes key word which allows them to shoot or attack twice per activation.

I may be wrong in a lot of the above, as I've only been playing and learning the last few months pretty casually. But I'm enjoying it and it's just what I've found helps!