Portugal in Sept?

September is a good time to visit.

There aren’t any tricks to getting a good flight, just monitor the prices and buy when you see something that suits your timing and budget.

You can easily spend 2 months in Portugal or more, but in 2 weeks you can see Lisbon, Porto and some of the towns in between.

If your concerns are about weather, go to timeanddate.com and pop in Portuguese cities and you can see the daily conditions for the month for any of the last 10 years. That will give you a good idea of what to expect.

Barring the unknowable consequences of Covid-19, I'd expect you'll find lots of tourists, and the earlier you go the the more there will be. I was there last year in late May to early June and crowds only impacted a very few places I visited.

You can see a lot in 2 weeks. There are fast trains that connect cities between Lisbon and Porto. Parts of the Algarve (south) can also be reached by them. Depending on your interests, a rental car may be a good idea for part of your trip, but you can plan a varied itinerary using only public transport - which is not expensive.

Based on my experience last year, now is the time to start booking rooms if you are a budget traveler.