|First of all, for a home situation you don't need VLAN's and in order to use VLAN's you'd need to buy expensive managed switches. It's not worthwhile for your home setup.|
How should i set up the 3 access points inside? Should i have 1 access point and the other 2 just relay the signal to reach all the way across the house (not sure if this is possible, my friend said it is, but i dont know)?
Yes, this is possible and when speaking about AP's it's usually referred to as "mesh" or "range extender" capability. If your AP's are capable of acting in mesh (range extender) mode then I would probably go that route. The alternative is to plug them all in and that of courses uses up network connections on your SOHO Router.
I assume i only need 1 ssid because i want to be able to walk around the house with a laptop and not force itself to reconnect.
Correct, it's one wireless network, so you want to only have one SSID
Should all 3 be on the same channel?
No. They would interfere with each other. What you should have is one on channel 1, one on channel 6, and the third on channel 11. This way, there's no overlap on the channels.
You will want your outside ones to be setup so as to overlap as little as possible since there will be signal spilling over to outside from inside, and vice versa. So, let's say you you put AP 1 (chan 1) on the south end of your house, AP 2 (Chan 6) in the middle, and finally AP 3 (Chan 11) at the north end of your house. You want to deploy the 2 outside AP's so as to not interfer you would put one on Channel 1 and set that outside at the north end of your house (nearest the indoor AP's on chan 11 and 6). The second one, put it on channel 11 and set it outside at the south end of your house (nearest indoor AP's on Chan 1 and 6).
I want to use both N and G at the same time, is this possible? How can i do this?
Buy AP's that are N standard but backwards compatible with G. There's likely to be either a setting to force it to use N and G, or, it's possible the default setting is for N and G. Read the manual.
For the 2 access points outside, i bought 2 air-ant2460NP-R directional antenna. The cisco rep said this will work with the AIR-AP1252G-A-K9, but i want to confirm with you professionals before opening the package
No idea as I've never used that equipment. Why did you buy directional antenna's in the first place? You could have just bought AP's to act as AP's. Directional antenna are more intended for point-to-point wireless shots. LIke say you have a shot 100 feet from your house and you want to connect them wirelessly. You'd buy two directional antenna's and mount one on each building and aim them at each other.
I suspect the antenna's need to be plugged into your SOHO Router in order to communicate on the network. Whereas the AP's you bought sound like their capable of a mesh. Mesh (extender) would work better as it wouldn't require making holes in your outside walls in order to run cables. Just put an AP inside the house real close to the outside wall and an outside one on the other side of the same wall and they should be able to communicate quite well.
Also, the cable that came with the antenna is only 3 feet long, can i get an adapter to make it 6 feet total,
If it's a network cable (ie: Cat5e, or Cat6) then it can be up to 100 metres (380 feet) long. Although, I wouldn't go over 80 m myself.
Third, is it possible to keep it the same ssid as the inside?
It's the same wireless network so yes, you'd want the same SSID.