There are a few ways around this. See if you can locate a very lightweight mirror. I have one that I got at a second hand shop. A lighter one will be easier to hang (you can probably hang it yourself). Another solution is to do a gallery wall with small mirrors included. Get from local second hand shops, thrift stores, and Salvation Army. I know it's hit or miss, but if you are on a budget, that's the way to go. Start a wish list for yourself. For other items in your gallery wall, look at the same types of shops. In addition, look at local art galleries. If you have more in your budget, get prints from art.com and have them printed locally. Another solution is to ask friends, family, neighbors, coworkers if they have any mirrors they don't want.

Your art selection is spectacular for the sideboard. A mirror over the sofa would have not been as successful unless it was a multi mirror installation. or a sunburst shape

Love the piece over the buffet, but it looks too tall for the space if that is a bulkhead above. I would use it hung 5" above the sofa and hang a round mirror in a complimentary style to your chandy over the buffet.

I think I will keep the picture over the buffet. I do like the 4th mirror, beverly. where is that from?

also, do you think it needs something with it to fill up the space?

This particular mirror has evidently been disc., but it was 63" x 63"

This one below is 39"