alfaz12, it's highly advisable to use a diferent address for each machine. This isn't from a technical viewpoint (technically you could use the same address) but simply so that you can easily identify what each machine is producing and, if you have queries or problems it's easier to pinpoint which machine the problems are occurring on.
You don't need a different actual wallet on all each machine however. You can create a single wallet on one machine, and create 3 different addresses with that wallet - one address for each machine. All your Infinitecoins mined from each of the 3 addresse will then go into that single wallet but you can still what each machine has individually produced.
Regarding the +numbers, these are the difficulty of pseudoshares that your miner will report (not to be confused with real shares that you get paid for). The pseudoshares help your hashrate graph at
http://treasurequarry.com:9844/static/graphs.html?Day show more accurately. If you don't include a pseudoshare difficulty after your infinitecoin address you won't get a good graph of your hashing...instead you would just get a single short and high blip every now and then.
External GPUs may suffer from a bandwidth (data transfer rate) problem in the connection to your laptop according to
http://www.reddit.com/r/apple/comments/1paw41/graphics_cards_in_new_mac_pro_may_be_user/ (check out just over halfway down where they start talking about thunderbolt). That particular thread is about bitcoin mining though which is sha-256 and gives a higher kh/s than Scrypt mining which Infinitecoin uses , so I don't know if Infinitecoin mining would be any better with an external GPU than Bitcoin.
We need more miners to improve pool's hashrate. I love this pool but it would be better with 20 mhash.
Tell your friends, family, pets and..well..anyone about Infinitecoin and get them to join in.

Another thing that I will like to ask , lets say if I am mining on three different mahcines, now as you told me to keep IFC Wallet on one machine and can assign different Address to other machines , now if I am getting the coins in the wallet , how would I know for what particular address i am getting it for . Thankyou