Is security of zk-SNARKS related to the size of the arithmetic circuit they evaluate?
I think there is not necessarily immediate relationship between security of zk-SNARKs and the size of the arithmetic circuit. Mostly the security of zk-SNARKs depends on your security parameter, your cryptographic assumptions and what kind of security properties you want to achieve. In contrast, the size of the arithmetic circuit is more related to the efficiency of zk-SNARKs, such as prover/verifier running time and proof size. For sure sometimes if you need some stronger security property, for example, you want to achieve universal and updatable CRS, this would lead to a larger arithmetic circuit