Filter Flow Rate

Delighted for you and the fish that you've made it through the fish-in cycle, BDS. Your commitment and perseverance following the poor advice from the LFS has paid off - well done! 

Yes, I'd just wait and see what happens. Hairgrass is difficult, crypts are very slow but tough, expect them to live but it will take a while for them to get going. Often a  tank the size of yours will look better with fewer species growing well rather than a lot of different types. Some will win, some will lose.

If the filter media looks disgusting, squeeze sponges very gently in old tank water. Just aim to get the worst off. If you have sponges that were white when new, they'll never be white again. And blue sponges go a purply colour. If you have ceramic media, just swoosh the container gently in old water. The biofilm where the bacteria live won't be fully established yet hence the need to be gentle.

You can drop off the testing. Maybe test for ammonia and nitrite every 3 or 4 days till you know they are staying at zero. Then once a month, then whenever you remember, or get new fish, or if the fish start behaving differently from usual.
Nitrate can be used to see if you are doing enough water changes. Test just before a water change and see how much higher it is compared to your tap water.

Once your plants start to take off, you don't need as many or as large water changes compared to a tank that has fake plants. Be guided by the plant people for water changes 

job well done BDS 

Do be gentle with the sponges, I've triggered a mini cycle in the past with an over enthusiastic sponge cleaning session

I now have some nerite snails and they're hoovering like mad so the tank is looking good, even the plants are in better shape.

Thank you for all your help along the way!