Firstly, Welcome.

The three items you have listed are designed to work together, in fact you shouldn't really run the DNA filters without a fuel modification, especially the Stage 3.

The Stage 3 filter hasn't really proved very popular, if you take a look through the forum some people have actually taken it off. The main reasons for this are;
1) it's gets damaged by off-road boots
2) it's benefits are for top end performance
3) it lowers your wading depth

You will need the both Stage 1 and 2 unless you are going to cut your snorkel off. The DNA cover is stiffer than a cut down snorkel, and in my opinion better at keeping a seal, but others have functioned perfectly OK by cutting out the snorkel.

You'll need to get a PC-V map suitable for the DNA's a few of us have this setup so a map is easily sourced, unless you want to put your bike on a Dyno. Obviously you'll get a more 'personal' map for your bike on a Dyno, over a 'standard' map (that isn't very far out anyway)

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Never underestimate the power of stupid people in large groups.