Re the Contact x2 it might be something to do with the template you selected when you installed it. note: the schema name has a prefix (standard out of the box Dataverse Tables do not have a prefix, other ones provided will usually have a msdyn_ or adx_ prefix the later is for the Portal) so has been created by a Solution with a publisher .that has that prefix defined (also if you look at Dependencies on it it may tell you the Solution it came from or you can look at the publishers and find the prefix then find the solutions from that publisher).
Generally speaking always use Account for Organizations and Contact for People. You can rename, change and extend them as you need. There is a lot of out of the box functionality based on Account and Contact - people who try to do there own thing around putting conacts/people in different tables usually end up with problems down the track. A person ideally should be represented in the system as 1 record (a Contact record), if they have multiple additional items then add them as 1:Many Child entities to the Contact record etc (or out of the box or manual Many-to-Many relationships as needed).
Unless heavily customized, the system does not easily support performing your own complex joins so if you normalize to a point where you have lots of Super-Sub typing types of structure you will find it difficult to bring get the info you need into views etc.
