"Tips for buying dining room furniture"

When measuring your room for fit, allow a minimum 36 inches around the table to have people seated and be able to walk around. For example: if your dining room is 9-1/2 feet x 12 feet then the largest table you can comfortably fit is 42 inches wide x 72 inches long. (If you want a hutch, then you will have to shorten the dimension of the table by the depth of the hutch for whichever wall you place it on.)
Tables can come in one of three heights with matching chairs/stools:

Dining Height (standard): 30 inches with 17 inch - 19 inch chairs (average 18 inch seat height)
Gathering Height: 36 inches with 24 inch barstools/counter stools (same height as standard countertops)
Pub Height: 42 inches with 30 inch barstools

Formal dining tables if they have any leaves will be regular (removable) and casual, gathering, and pub tables will usulally have self-storing leaves (also known as "butterfly" leaves)
Most dining tops are built with MDF or other fiberboard/plywood for a flatter, more stable construction. This is then covered with a real wood veneer. MDF also prevents splits along the grain of the table top which is more common with solid wood construction. Very few tables are still made with all solid wood.