The site that most of us use for information on fish species is https://www.seriouslyfish.com/knowledge-base/Also were do I go to get accurate information on what parameters and tank sizes certain species need.
As you are in the UK, look at Argos play sand. Some of the sand other members have mentioned are only available in the US.
If you intend a planted tank, provided you have more than just the odd couple of plants, you can do a plant/silent cycle as plants take up ammonia as fertiliser. With this method, the tank is planted then we wait until the plants are showing definite signs of growth. The last thing you want to do is get fish then the plants die. Once you are sure they are growing, then fish can be added one species at a time. To be on the safe side, test for ammonia and nitrite every day after adding fish. If they stay at zero, the next species can be added after a week or two. If either show up a water change is needed to get them down to zero.
With this method ammonia is not added. Fish make ammonia in tiny amounts every minute of the day so the plants remove it as soon as it is made. Adding a dose of ammonia in one big dose can harm the plants you are trying to grow.