First, what do you need light for? Do you do paperwork? Is your desk in your window? You'll be getting afternoon sun. I'm recommending LED lighting to people, but Fred says it has a way to go in brightness and affordability. I recommend sky tubes to homeowners. I've had 2 in one of my houses.

There are lots of guidelines on the internet about rug sizing for dining areas. They advise a certain number of inches behind each dining chair so the legs stay on and so people have space to move around - just look those up and then apply to the dimensions of your table

Yes, I agree with Beautiful Abode. One metre (between the back of the seat and the wall or passageway) is required for someone to be seated whilst another can get behind them to access the next seat along. Proportionally, 1.2m x 2.4m is a good proportion for a dining table for 10, which means the person's place at the head of the table will not encroach on the placing of the two diners on either side. Also 1.2 is more generous for serving to the centre of the table. There is no hard and fast rule to dining table dimensions. However, if you table is 1.0m or 1.1m wide, you will need to allow for a little more than 600mm per person in its length. Best way to test the ideal table size for you is to get some table mats and place them on a table as far apart as you feel most comfortable, then ascertain the table size by drawing a line around them.

You could go wider but it depends on what type of dining furniture would want to use and how many you will be catering for. Bench seating tucks underneath and when it is being used you aren't so worried about the other space. You could always turn it around the other way [ perpendicular to the house] so the width is less of an issue as 10 metres is a decent length deck. I think even an extra 30cm would make a difference and not doing it may cost more in regret than the materials. You could go wider in the dining area only but it is a bit hard to judge without seeing the space. Find some furniture you like online and map out a plan for yourself - use newspaper for life size modelling. Good luck