On whether you need a lawyer, the answer is “no”. The application can be filed with the United States Patent and Trademark office online. Just take your time, and make sure you choose the international class(es) for your service, and make sure your mark isn’t merely descriptive (e.g. “HOUSE CLEANING”).
Not sure if your service is regional or national, but perform a search to see if anyone has registered the service mark here. You want to ensure there isn’t a likelihood of confusion with anyone else’s trademark.
For a trademark registration to remain valid, an Affidavit of Use must be filed after the fifth year and the registration must be renewed every 10 years.
Filing an electronic application with the US patent and trademark office costs about $275.