I've never used this particular device, but I am familiar with wireless bridges (and have used a few)
Yes, your server will get the IP in the same subnet as the other computers (provided its set up as a bridge)
Yes, you can port-forward in your router. A bridge is like a switch, ie sits below the TCP/IP layer, so this will work fine.
A bridge will slow down your connection quite a bit (the exact speed of the connection
will, of-course, depend on the strength of connectivity etc). You should be able to connect multiple (ie more then 4) devices to it. You are unlikely to be able to push 100 megabit through this though.
That said, you might want to look at getting an AP Client (access point client), which will do the same thing but not try and repeat the signal wirelessly. DD-WRT has good support for this - so consider getting a router which works with DD-WRT and using that. When I set up a bridge, I landed up purchasing 2 devices which spoke on both the 2.4 and 5 gig band, and used the 5 gig band to bridge the network together in 2 parts of my house - of-course, this assumes you can get 5 gig coverage to your garage.
Another thing to look at as an alternative might be a couple of ethernet over power devices - these are likely to be more reliable as less subject to WIFI interference (and also appear as a bridge). I mention this because you mentioned its a server.
thanks for that. if i use ethernet over power , then can i join that ethernet port to switch and then attach multiple devices – user1721949 – 2014-03-27T05:05:16.533
Yes. Think of a couple of ethernet over power devices as being a long ethernet cable, or if you get one with a switch built switch, think of it as daisy-chaining switches. – davidgo – 2014-03-27T06:56:24.413