I've been working through ISIS since I'm not very familiar with it. ISIS by default creates Level 1 (intra area) and Level 2 (inter area) adjacencies with other ISIS routers. You can limit the type on a per interface level ['isis circuit-type'] or on a per process level ['is-type']. Same with authentication, you can do on s per link or on a per process level and authentication supports clear text as well as MD5 hash.
Level 2 is considered the 'backbone' area as all other level1 router need to connect and transit a level 2 area to get to another level 1 router. Level 1-2 routers automatically redistribute level1 prefixes into level 2. In order to redistribute Level 2 into Level 1 you need to configure 'redistribute isis ip level-2 into level-1 route-map/distribute-list'. The route-map doesn't need to contain any entries, it just needs to exist.
Default-information originate by default will originate only a L2 default, in order to generate and L1 default create a route-map, set level level-1 and then append the route map to the default-information originate.
Metrics, without metric-style wide configured, isis defaults to max metric of 63, enabling wide metrics lets you go far beyond that. The default metric of any interface is 10 and can be changed.
Priority, the default priority is 64 with the max being 127. Priority is used to determine who will be the DIS on a multi access segment like ethernet.
Summary-address, can summarize groups of addresses for a given level. The metric used to advertise the summary is the smallest metric of all the more specific routes.
