Below you will find an excellent step by step for implementing a clustered issuing CA :
To answer your questions in the ca cluster you will have an active node and a passive node as far as I know so your client will request the certificate from the active node.
Because they will share the same database the passive node will be able to renew client machine certificate if the active node go down.
The 2 CA will share the same CA name
The other option can be to have multiple issuing ca but the issue with this configuration is during certificate request the first one to respond will issue the certificate for your client if the same template exist on your 2 CAs. The good news is that you can use enrollment policy service to build the list for your client.
For the renewal I'm not 100% sure but it will follow the same principle of the issuing part build a list of issuing ca and check if they support the template issued