1. Yes its same as that on the primary poller (same instructions to be followed for additional poller as well), but then you will have different bits for the additional poller with the same version (NPM/SAM) - I am not sure if you have separate additional poller bits for IPSLA MGR (Currently its VNQM), in case you don't have separate additional poller bits for IPSLA MGR use the same bits that you use for your primary.
2. As you have mentioned I have my upgrade increment path worked out, im sure you would have checked on the upgrade path (Helpful link attached below).
3. Just make sure you take a DB backup, shutdown services on additional poller and primary poller. Upgrade NPM on primary poller, once upgrade is successful it would automatically start orion services on primary poller, keep them running. Move to your additional poller and install additional poller NPM bits of same version, follow the same steps as you did for primary.
4. Once you are done with installation of NPM on primary and additional, move to the next module SAM and then IPSLA MGR.
Helpful link:
SolarWinds Knowledge Base :: Compatibility of SolarWinds Orion Products for Installation and Upgrade