Spinning up another server for SSRS would require additional SQL licenses. But if your covered until the unlimited virtualisation rights then that shouldn't be a problem, if not it can get costly.
Again how you implement it is difficult to say as we are unaware of what your reports will be doing.
Realistically you "should" be spinning up a dedicated SSRS box to keep all the HTTP traffic away from the SQL server(s), they just don't need that extra overhead, and then you can squeeze as much resource as possible out of the SQL engine services.
Readable secondary's again, comes down to licensing, you have to license the servers your reading from. Again if your all VM's and have unlimited rights, your fine, otherwise, again costly.