It is difficult and dangerous to combine aluminum and copper wiring. Are there any pitfalls with respect to tinned copper and copper?
Tinned copper is fine to splice the same way as ordinary copper
Tinned copper (silvery on the outside, copper-colored on the inside, oft stranded) is fine to splice using copper-rated splices. This is not to be confused with aluminum (silvery all the way through) which requires special splicing (Alumiconns or AlxCu mechanical connectors), or copper-clad aluminum (copper-colored on the outside, silvery on the inside) which also is OK to use with copper-rated splices, but needs to be treated as aluminum with regards to wire gauge.
So you have 2 questions tinned copper and copper are fine to combine no problems there but copper and aluminum are a totally different type of connection requiring the use of special connectors. With aluminum and copper the junction will fail if not done properly causing a fire hazard. Tinned copper and copper a wire nut is fine. Look up aluminacon connectors for aluminum to copper connections.