Thanks for choosing Malawi for your upcoming grow.
I'm not familiarized with the brand of your soil so i cannot comment on this one, but I always recommend the same standard soil mix as a base: 80-90 % of high quality peat, 10 % of worm casting and a fistful of guano in powder for every 7 liters of soil mix. You can also add other additives and mycorrhiza you are used to work with.
As described in the growing tips of the official strain description, we recommend moderate PK levels for the whole cycle, and slightly lower of nitrogen. Typically you can start them with an EC of 0.6 for the first 3 weeks of life, increase up to 1 or even 1.2 EC for late veg/early flowering stage, and around 1.2-1.4 EC (for the tinner leaved Old Malawi Killer phenos) or even 1.4-1.8 EC (in case you have New Killer phenos with wider and darker leaves) when Malawi is producing most of her flowers in flowering stage.
PH for soil, watering and feeding must be between 6.5-6.8.
Anyway, if you have any doubt during their development you can always email me or post your progresses here. Best wishes!