Well, the happy thought from dining in a good room is not based on the number of tables in it, but rather on room value. Drop a platinum artefact cabinet in your single table, single chair dining room, and any dwarf lucky enough to get to dine there will be ecstatic.
However, having too little tables does incur a negative thought of it's own. When a dwarf is grabbing food to eat, and it cannot find a table, it will get the 'was annoyed by the lack of tables' thought. When the dwarf can find a table, but not sit down, I believe it will get the 'was annoyed by the lack of chairs" thought. Those negative thoughts are pretty minor compared to the positive boost of dining in a royal dining room.
I have about 8 tables and chairs in my single dining room. It seems to be about enough for my 54 dwarves, as I rarely, if ever, see the negative thought for lack of chairs/tables. That's because dwarves don't all eat at the same time. So they all get their happy thoughts for dining in a royal dining room, even if there's only 1 table for every 7-8 dwarves.
Same goes for beds. As long as you keep to general sleeping area's, and do not assign personal rooms except for those pesky nobles who demand one, you can do with about 1 bed per 7-8 dwarves as well.
I tend to assign every dwarf their own bedroom with cabinets and coffers though, so they can store their personal stuff.