There aren't a lot of extra vacant apartments in the Portland area. Compared to the national average, the rental market is tight in this area. In most cities with markets like this, and Portland is no exception, looking in November and December is a good idea. April and May can also prove good results.
Convincing a Portland landlord to rent to you is going to be made easier if you can show that you already have employment or an educational program lined up in the area. If you can prove this, the rental process will be fairly straight forward. However, with the rental housing situation being tight, if you're not working or studying in the area, it wouldn't be uncommon to face a few questions about why you've chosen to relocate to this particular city.
Although there is a small public transportation system, it is definitely not the best option for getting around Portland. If you're sticking to the downtown area, walking will help you avoid the often-congested traffic. If you need to get to the outside areas of the city, you are probably going to need a car during your stay.
Several historic landmarks in Portland are worth a visit, including the Victoria Mansion and the Portland Observatory. Several beaches in the area are popular recreation areas, and numerous options exist for getting out on the water for sightseeing or fishing. Head to the Old Port neighborhood for the best shopping and dining in a quant, historic setting. The best local beer bar is The Great Lost Bear.