If I redirect them to the .com will I get punished by the search engines for having multiple sites pointing to only one or do the search engines accept this as normal business? Should I just leave them empty or is that also a bad idea?
Of course, doing an actual trademark application will help if someone uses your name without permission.
The main problem becomes and industry one. A trademark can be extremely costly since you need to pay for EACH sector you want the trademark to apply in.
For example: You open up a general store and trademark "Widget Town" for that purpose only. Some other guy starts up a comic book series called "Widget Town". He buys the .net or whatever. Do you have a valid claim? No. You registered no claim to the name in the sector he is operating. You can always spend money and try the case in court but defeat will be the most likely result.
If you do a search on some big names like Federal Express, Wal-Mart, and so forth, you will see how they spent lots of money to trademark their names in just about every possible category.