Stage Magic can be a difficult beast to tackle since most sites sell effects that are garnered more towards street magic audience sizes. You are at a huge disadvantage by not having a live feed being projected on screens for the whole audience to see close-up magic. That is fine though, there are plenty of different effects that I know and can personally testify for the strength of their material.
I've done one show about this size before at a magic convention with an illusionist named Joaquin Ayala but more commonly goes just by Ayala. We didn't have a live feed either but the gymnasium was packed so we knew the material had to be dramatic for everyone in attendance. Ayala is a master of performing illusions and performed some his best work including the fiery swords, the floating butterflies, and his famous spears act which is what I mainly helped with on stage. All parts of his act were big and visual and had a drama element to it to keep the audience intrigued. I highly recommend finding something that will keep your audience on the edge of their seats waiting to find out what you are going to do next.
If you are looking for good stage mentalism, I couldn't recommend Sheer-Luck by Shawn Farquhar more. It is a great comedy routine that has a wonderful surprise at the end and plays well for an audience of any size. You will be at a visual disadvantage since you won't have screens running but your interaction with a spectator will more than make up for that.
Really anything by Scott Alexander will give you an edge in performing. I have almost his entire release library and can easily say he's one of the greatest creators of our time. I personally met him and Puck at a convention as well and they are wonderful people. His material is very expensive but the payoff is more than worth it. My top recommendations for your show are Nailed It, Hanky Panky, Shoe Business 2.0, and if you can find it; the Final Answer. I know all the methods to all of those routines and can guarantee you they are 100% safe and sure-fire effects.
I recently got into escape art and escapism over the last year or so and give highest recommendations to In/Out Rope Escape by Tony Clark. His full routine he teaches is sure to keep your audience engaged with your act. He also tips off some great comedy bits. I also will sometimes strip down to my swim trunks and pull off the Houdini Chain Escape blindfolded. The full set comes in separate pieces but it visually looks amazing and threatening to be chained up at the neck, ankles, wrists, etc. and then escape while blindfolded. Your partner will need to hold up a curtain though.
Lastly, there is always the spook house illusion that Scott Alexander teaches in his third penguin live lecture. You can make it yourself for cheap or buy it from a magic shop for around $175.00. It requires two people and your audience will love it.
With any stage magic routine, make sure you rehearse your butt off! You and your partner will have to get every cadence and movement down to muscle memory. Have your lines fully memorized and remember to always pause for laughs. Lastly, have fun with it! There is nothing more exhilarating than perform for a large group of people on stage and causing them to react to your show. It has now become an obsession for me. Best of luck!
