What schema and tablespace you choose depends largely on the usage of the tables when they are created - if they are likely to have high transaction rates against them, then it is probably a good idea to create a dedicated tablespace for them, preferably on a seperate disk (the usual recommendations for seperating data and indexes apply here as well). If they are likely to have a low rate of transactions against them, it is safe enough to put them in a tablespace with other data. (It is still a good idea to seperate data and indexes into different tablespaces, with the datafiles for each on different disks).

The user that is used to create the tables is entirely up to you. You may want to create a new user as a fairly simple means of keeping the data easily distinguishable from other tables (e.g. you can export an entire user, if you have a user dedicated to owning this data, that can make it easy to export only this data). If you do create a new user, be sure to specify a default tablespace and temporary tablespace. If you do not, the default place for object creation and temporary sort segments is the system tablespace. This is a bad thing.