Having a total substrate depth of about 2.5-3" really helps.
Even with the bags not having much in the way of bigger organic material the potting mix will still collapse a good bit the first year so save some extra capping material tucked away to add later as needed.
Looking forward to the updates.
The Fraternity of Dirt
If at first you don't succeed,,, keep kicking it RubberSideDownOnTheLanding, 2-75g planted, 5-55g planted, 5-20g planted, 110g w/30g sump, 8-10g, Refugium, doghouse/newbie 2012 update adding table top pleco pans & a 90g (Nutz)
The "dirt" is just the fine grains that will end up clouding the tank and then get removed by the filter/water changes anyways. I highly suggest rinsing as well, I thought I did enough and it was still a bit cloudy and I didn't even use it for the entire substrate.
Really doubt you'll be washing away much of anything other than the smaller particles. Seachem says it's ok...
Although pre-washed, it may be rinsed before use to remove residual dust. Dust can also be minimized by filling aquarium slowly and dispersing water so that the Flourite® bed is not disturbed. Slight initial cloudiness is normal and will clear rapidly (2–12 hours). To shorten the cloudiness period use Clarity™ in conjuction with mechanical filtration (such as filter floss).
But you can minimize the dust and take care of it later if you want.