The basic question I'd ask is whether you want to leave the table full size all the time. A table for 10 is pretty big and if you have less people than that, the meal is not quite as intimate with everyone sitting on one end. Also, a 48" wide table makes it tough to pass things across the table - people may have to stand and lean over to pass plates and bowls across the table.
The other choice is to go longer but stay about 36" wide - but then the table would have to be 12' long. Don't know if that would work for your space. The best thing would be to mock up the table with sawhorses, some strips of wood, and kraft paper to represent the top (staple the kraft paper to the wood strips). That way, you can see what the table will look like in your space and how it looks to sit across it.
I agree that the best way to make the top is to use veneer and a stable substrate - maybe some really good baltic birch - then put an edging around it to hide the plywood. Put edging where the two halves meet so you don't see the plywood and lay the veneer over that edging. Personally, I really dislike breadboard ends (for a number of reasons). Regarding leaves, you need to decide whether you're going to have the leaves in or out most of the time. If they're going to be out (which is usual) lay your veneer so that it matches with the leaves out. Very often, when you put the leaves in, you're going to have a table cloth over the table so you won't be able to see the grain match between the main table top and the leaves. But do use veneer from the same batch for the leaves so that you get a good color match, even if you don't get a good grain match. Even when you do that, the wood ages differently because the leaves are stored out of the sun while the table is in the light and ages (darkens or lightens).
Regarding the table slides, buy those. You can make them but it's a specialized job and the pros will do a better job than you will.
Putting a couple of legs in the middle of the table is a good idea for a table that big and should not be problem to design in. Put rollers under those legs so you can open and close the table easily. A nice touch is to make the two legs fit together when closed (no leaves) so that they look like a single leg.
Oh, one more thing. You need to decide whether you want the apron continuous when you have the leaves in, or whether there will be gaps in the apron when the leaves are in. Having a continuous apron looks better and people don't hit their legs on that corner of the "broken" apron, but putting apron parts on the leaves requires more storage space for the leaves. If you go for apron parts on the leaves, I'd follow what you do for the top - that is, if you make the grain match without the leaves, make the grain match on the apron the same.
That's all I can think of right now. Good luck! A big table is a challenge but when well done gives a lot of satisfaction both to you, the builder, and to the user.
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