You'll have a good time. Being at the first turn means you'll experience a Race Start, and you'll have a great view of T1, the next straight and then likely quite a bit of the middle sector. Use the Friday and Saturday to experience anywhere else on the track you can view from and try out the amenities put out for spectators, because by Sunday you'll want to avoid all of that. Make sure you have plenty of drink with you and something to keep you warm, because it's amazing how quickly a bit of a wind can cool you down in a grandstand. Admittedly when I was there with was 38°C so I got badly sunburned. Bring good suncream if your skin is light enough to be susceptible to that.
For Sunday, I'd say get there early and get in your seat. The F3 race is first and early so make sure you're there for that. Then you're best to stay for the day and just enjoy everything. You'll get to see the card on the grid and see 20 of them accelerating off the line. I have been by the start line for 3 Grand Prix to see that start and it is an incredible sight. Have a good time and post photos here!