Do you want a centerpiece that can be kept on the table all the time like while eating or do you need the table space and would like something that can be removed?

I would like to put something rather large on the table as part of the decor (I hardly use the tablet). My kitchen, dining room and family area are basically one big room. A bowl or vase look small on a large table in a large room

I am still looking for suggestions

here are a few ideas I found. The lighting is low in all of these diningrooms. Also , have you thought about turning the table the other way? That would give you more room between the wall and the window . Also, I think you might add some colour with a rug.

here are some accessories
https://www.jossandmain.com/Wine-Country-4-Piece-Orchard-Decor-%26-Tray-Set~IMX7639~E8509.html
https://www.jossandmain.com/Country-Kitchen-4-Piece-Enchanted-Owl-Statuette-Set~IMX8792~E8743.html
https://www.jossandmain.com/Allister-Home-Dunning-Candleholder~BAIL1055~E8496.html

Bowl of apples.

I do not think that something really big will look right on this table.

How about a large hand-painted bowl? http://www.etsy.com/listing/167624581/yellow-navy-orange-large-bowl-handmade?ref=sr_gallery_28&ga_search_query=large+hand+painted+bowl&ga_order=most_relevant&ga_view_type=gallery&ga_ship_to=US&ga_search_type=handmade

I would use a long, low, oval, white bowl (about 18" long) with some colored items. Maybe with large sea shells or plant pods. Fill with something large enough in irregular shapes. A large item as a centerpiece will be the correct proportion for your table. Small items will become lost.