How to migrate an existing Proget instance safely to a new server (under IIS)?

I'm migrating our Proget instance (v 3.8.5.3) to another server. I've already got other websites running under IIS on this new server, and I want to run the Proget instance alongside those as an IIS-hosted web app (port 80), just like I did on the old server.

I've already migrated the existing database, and I've already created the proget web app instance on IIS (which runs with a dedicated App Pool Identity).

Q1: How do I tell the installer to setup the Proget web app under the already-configured IIS website instance? The biggest obstacle seems to be that if I select "IIS" option the installer then wants to know which account to run as -- obviously I want it to run as the App Pool Identity I already configured.

Q2: I'm also concerned that, if I point it to the existing database, the installer may wipe out the existing data in the database, or that there will be a version conflict if I try to use the 3.8.5.6 installer. Is there any risk here? Should first I use the 3.8.5.3 installer and then upgrade?

Product: ProGet
Version: 4.0.4

To migrate ProGet to a new server is as follows:

If you're using a local database, back it up and restore it on the new server
If you're using a local package store, copy those to the new server (ideally same exact path)
Install the same version of ProGet on the new server, pointing to the new database
Change whatever IIS settings you desire
From the web app, edit whatever settings may have changed from the Admin section