You're in luck! Britannia is actually one of the best documented Roman provinces, due to a variety of sources which are mostly unavailable on other areas of the Empire. A lot of these sources are also extraordinarily well systemized and described by academics, so they are accessible and available for research.

These sources are:

• Literary: Roman writers, such as Caesar (like you mentioned), Tacitus and Pliny the Elder, who all wrote elaborate descriptions of the island. These sources are quite unique because there weren't usually a lot of Roman writers interested in writing about a faraway province. You can find their works anywhere online in translation.

• Inscriptions: the inscriptions of Britain are also exquisitly well documented in the database Roman Inscriptions of Britain (https://romaninscriptionsofbritain.org/). There are a lot of them and they cover almost every subject imaginable. Other Roman British writings include the Vindolanda tablets, a huge collection of wood shavings with writing on them, found near a fort on Hadrian's Wall. The Vindolanda tablets too are unique because they represent the everyday communication of the civil population and the army. They concern literally everything, from sending more underwear up to the fort to lists of soldiers available for service to birthday invitations. You can find them at http://vindolanda.csad.ox.ac.uk/. Finally, there's the Bloomberg tablets, a collection of wooden tablets found in London. They predate the Vindolanda tablets and are also mostly everyday communication. However, they are a pretty recent find so they are not yet as neatly indexed as the other sources. There is no database yet.

• Archeological: this is a very broad category. Concerning landscapes, there are surveys, air photography (so seeing the outlines of sites you wouldn't normally see from the ground), pollen research (to determine forestation rates and other agricultural information). Concerning humans and animals, there's bioarcheology, so research on bones, teeth, bog bodies, and DNA research has also newly been introduced in these studies. And then there's of course material archeology: what's left of buildings, coins, other images like mosaics, pots, pans, the usual things. I reckon the British Museum will be your best friend in this category ;)

I don't know if you have access to academic sources. If so, the major journal 'Britannia' publishes exclusively on Roman Britain and has done so for over forty issues, wherein almost everything I've mentioned has been covered at one time or another.

Do know that a known problem of the sources listed (and a lot of antique sources at that) is that they will not provide you with a picture of "the economic system of Roman Britain" or an answer to "How do politics in Roman Britain work". These sources, especially the written ones, are usually more on the everyday and 'human' level. They will tell you a lot about individual cases and people, but the big picture is difficult to construct. The Roman authors who tried to do so are usually to biased to be taken completely seriously as an authentic historic source.

Good luck with your research!