First tip: If you haven't yet got the interpretation guide to go with the standard then I'd unequivocally recommend doing so.
Second tip: there is a lot more advice available on this forum and on the internet in general for BRC Food than for BRC Agents & Brokers 
Therefore worth seeking out guidance on the corresponding BRC Food clause, as there is a lot of overlap between the two standards and much of it can be translated fairly directly (although Agents & Brokers has a few unique peculiarities...).
I posted a document here that can help finding the BRC Food clause that corresponds to the Agents & Brokers one, that might be useful for you: https://www.ifsqn.co...clause-mapping/
Looking in more detail at your specific questions:
Nature of product and associated risks
For meat this is likely to be temperature-related considerations, possibly veterinary chemicals/residues (meat is a long way from my area of expertise but if you look for guidance on this area for the BRC Food standard it will likely turn up more detail!) The species contamination bit probably lives in the adulteration/fraud category.
Customer-specific requirements
I think you're pretty much on the mark with e.g. RTA, potentially organic, free range, only allowing supplies from specific origins, particularly welfare standards in place etc
Legislative requirements in country of sale
Assuming you're only selling in the UK, your life is a bit easier as you don't (yet) have consider multiple regulatory regimes. There is still the consideration of e.g. requirement for approved premises for abattoirs etc. in the supply chain that I'd suggest documenting consideration of. On a slightly pessimistic note, I'm reluctant to mention the "B word" but now that it's done I will be including this in my next HACCP review, as Brexit does pose a real risk of regulatory divergence from the EU, which won't make our lives any easier in the food industry...
Source or country of origin
If you're only importing from the EU then I think you can reasonably claim that the risk factor is fairly low - as a parameter to consider it becomes far more relevant with a global supplier base where there is genuinely significant variation in multiple ways.
Potential for fraud or adulteration
This is an interesting one as you can potentially attack it in two way - either via a generic risk status set in isolation in the supplier risk assessment (possibly the weaker approach), or by directly using the output of your vulnerability assessment required for section 4.8 / security assessment for 4.3. The latter is undoubtedly going to be the stronger approach, but potentially also more work depending on how many different products (or groups of products, if you can sensibly cluster products into groupings with comparable properties) you have to manage.
Generally you're on the right lines here I think - falsification of label/code details, shipping/import documents, substitution/adulteration of products etc along with the potential for malicious tampering in the supply chain.
