Bing search engine in the UK shows an OS map view. Use it, it’s much cheaper than buying the maps. Don’t think of not using OS (or Harvey) maps, it’s part of the British outdoors.
In Scotland you can camp where you want, away from roads etc. In the upland areas of England and Wales it’s not strictly legal but is widely tolerated if you stay away from farmland and out of sight of roads/buildings. Make use of this, as it’s free. Don’t stay in one place more than a night (except in Scotland).
Most of our outdoor areas don’t have tree cover. And it’s quite windy. Get a decent tent.
Use MWIS for weather forecasts, but even now they aren’t very accurate - that’s life.
If you have a car stock up with food in places like Lidl and Aldi, much cheaper than the little shops in countryside villages.