Vinni,
there is more than one answer to each of your questions. I would suggest you read up on the inner join definition first. My advise is to use the inner join when you need to return equal values in 2 views/tables. the performance will be degraded based on the size of the hardware, the number of records in the process, the number of records in the output, etc. (many factors)
Calculated columns are used when your data does not contain the value you need. it is ok to have calculated columns, however, you need to know where to use them. Again, more than 1 answer to your question due to the fact that it will depend how many tables/views are involved in your model.
One thing I'd recommend is to push filters down in your model so that you reduce the number of records and do aggregations above so that you minimize the operations in your data model.
hope you have good luck on your model