If you use a mail forwarding service, you change your address on everything to the address given to you. All mail is sent to your mail forwarding service. The service then sends your mail to you when you request it and at an address specified by you. This is the type of service that many full-timers use. If you are needing this for only 6 months, I don't think I would use mail fowarding as you actually have to change your address on everything. The postal service premium may cost, but it's probably the best way to get all of your mail.
Unless you put in a permanent change of address you will not receive mail that is designated as do not forward or address change requested which is usually most of your important mail. When we did the temp address change to a private mail box (UPS store) all of our 1099 and credit card stuff went back as address correction required, didn't have a clue until started getting calls requesting our new address. As yet still haven't found a perfect way to do this.
The post office will forward the mail. But, if the letter says " do not forward" or words to that effect, it will not be forwarded. The first year we snowbirded, we missed some bills from a doctor, because of that. Also, we had trouble getting some annual enrollment papers from the insurance companies. We try to do all of that online now, but some places just aren't online yet. Now we rent a po box, and use the premium forwarding from the post office. This gives us all our mail. It is pricy, though.
They will forward First Class mail only. Any junk mail gets thrown away. Magazines will be forwarded by USPS for only three months. Best to change the address with your magazine's publisher.