??? My First Classical Concert,What Can I Expect ???

I would try not to build it up. Try to enjoy it. Attending a classical concert in an acoustically wonderful 1920's concert hall with a world renowned orchestra can be an incredible experience, assuming you like classical music. 

The acoustics in a church will be unusual... so, perhaps look at it as an opportunity to experience very strange acoustics. Placing a small orchestra (early classical pieces are done with small orchestra's as opposed to Beethoven and later) is likely just to sound unusual. Good that you are up front so direct sound is likely to dominate. 

Anyway, if you are interested by this experience, travel to a major city and go to a great symphony hall. In this setting you can experience the very quietest sounds to over 100db in great crescendos of some of the more modern works. 

I've been to hundreds of symphony concerts. I spent many listening to the acoustics as well as the works. I really enjoy them. Hopefully this can be a gateway for you. 

All good advice above. You will hear natural sound staging, not this over precise image placement we hear with so many recordings. Natural timbre, micro and macro dynamics should also impress.   Hearing non amplified instruments with little or no sound reinforcement provides a unique perspective and may provide a new reference for what one is seeking with their home system.

From an audiophile standpoint, you will be amazed at how NOT BRIGHT a live orchestra is. ;-)  I think unamplified symphony concerts are very good for training your ears toward a more natural sound.  On a musical level, you'll be thrilled by the sound of a massed orchestra.  On a few occasions I've had the amazing experience of performing as a voice artist in front of a symphony orchestra.  The experience was indescribable!  Finally, you will love the Brandenburg Concertos.  Tuneful, danceable, moving and uplifting music.  Enjoy!

@dogearedaudio 

+1

If you can, I would sit back in the hall a little further.