If you want to be more flexible with your guests, pay attention to the leg width and where the legs are placed. In general, a table with thinner legs, or where the legs are at the corners, will make it easier to squeeze an extra chair in.
While its important not to go over the top, a well-presented dining room will always have an injection of colour. It doesnt have to be bright yellow. It could be a subtle light green with matching curtains that have a pop of pink in them.
If you fall in love with a metal or marble table, don’t be discouraged from buying it, but do think about how you might safely transport it. As suggested above, choose a small, round marble table, or go for a wooden table with detachable legs.
It is likely that you will take the new items with you and so it wont be a wasted spend and could end up selling your home if it helps to make the room appeal to buyers. If you dont take them with you and the buyers like the space, you could offer to sell them - this is particularly handy for first-time buyers.