A table top can be any size you want it to be. I agree, larger the better, simply due to the fact that you have support and as you've pointed out, assembly purposes.
I suggest you take a good look at OP's table top and look at Rocklers tables too. These will give you a very good idea on how you may wish to go for mounting. You won't be dissapointed if you go with a plate instead of mounting directly to the table.
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