Re: trigger question
First, it all depends on what kind of shooting you are doing as to which particular trigger may be best. Certain competition shooting events require a certain weight of pull, etc. If you are just "plinking"...then anything goes.
Second, the trigger you select will dictate whether you want to have a professional install it for you. Many improved, match-type triggers are "drop-in" and can be installed by anyone with familiarity with disassembly/reassembly of an AR lower. Others, such as some highly adjustable triggers, may require a pro depending on your level of experience and comfort with the job.
I always recommend the Giessele triggers. They are first-rate, and arguably one of the best triggers on the market. They run $250+ for a fully adjustable, 2-stage unit while they offer a non-adjustable match trigger for around $170. Also take a look at the Timney 1pc drop-in trigger units. These are another excellent trigger option, available in 3lb and 4lb versions, both for around $180.