Re: Bike advise
Bikes can be like cars in that they have new editions every year. So a nice used bike can be had at some savings.
You stated commuting and trails. A nice front suspension bike (hard tail), or hybrid would do nice. Dual suspension are fun, but unless you are riding extreme downhill, you can do without the extra expense and weight.
Next is the material, the cheaper bikes are chro moly, they are rigid and rugged, but can also be heavy. If you can get a used aluminum for the cost of chromoly, then get it.
I have an older Cannondale F5, although I dont ride as much as I used to, this bike never quit on me. Easy shifting, disc brakes and I purchased two sets of rims and tires so I can could commute and ride trails (street and offroad tires). You really dont want to ride offroad tires on pavement, it wears the tread and can slow you down.
So anything from Cannondale, Trek, Specilized, Kona should serve you well.
Lastly, you may think you know how to ride a bike, but learning about the proper fit, seat height, peddle clips can make life much easier.
Be careful with bikes, they are as addicting as rifles.