If you not going crazy everyday I think 500 euros is enough. Again, food and drinks are pretty cheap there so I think 500 is fine. I had more than a few good hearty dinners that were under 15 euro. Depending on your spending you MIGHT go a little over 500 but not by much.
Subway from the airport to the city. After that we mostly walked around. We used uber a couple times and it's pretty cheap, avg price was like 5 euro a ride. Also took the tram/streetcar once or twice.
Yeah, most people speak English so there's no language barrier really.
Do you know where about you're staying?
Staying in Lisboa old town right by a subway stop anjos I that according to google maps takes me downtown in like 15 min
Thanks for the tips seems much more affordable than when I was in London in April.