The speed of the ports refers to how fast you can transfer files and total bandwidth available over hard wired LAN. If you only plan on using the wireless portion then you don't need to really worry about how fast the ethernet port speed is.
The routers that don't advertise speed or frequency are cheaper routers that you can count on being 2.4ghz and either 54G or 150N speeds. That D-Link is a cheaper router only designed to have connections "up to" 150Mb per client but transfer speed wont actually be that fast. For instance, maximum speed capable of connecting will be 150Mb on the router, but if you have a 300Mb or 150Mb N card in your computer chances are you will connect at slower than that. If you buy a "dual band" router that means that router can handle clients on the 2.4ghz and 5ghz frequency range simultaneously. The advantage of being in the 5ghz range is you wont get any kind of interference by devices like other routers, microwaves, or home phones that run in the 2.4ghz range. Being "dual band" just means that particular router has 2 different radios that handles clients on both at the same time. It's like having 2 subnets (literally) on the same local network.
Speed on a router is how much total bandwidth you have and how fast a client connects. If you have a wireless N 300Mb router, and a 300Mb wireless card for your PC then you have 300Mb worth of bandwidth to use on the down and up stream. So literally speaking you can transfer at 150Mb up and down at the same time, or get full up to 300Mb down or up separately. To give you an idea of what I'm talking about in literal terms is this.
A hard wire ethernet connection at 100Mb can handle around 12.5MB/s theoretically (1000Mb gigabit is around 125MB/s max bandwidth), but actual transfer speeds are around 10MB/s. If you have a 300Mb N router, a 300Mb N card in your computer, if you are downloading something from another computer you can transfer up to 37.5MB/s, but will probably average more around 25MB/s. If you are uploading and downloading at the same time split that in half. Remember, these are all based on theoretical "up to" speeds which is the maximum capable of each piece of hardware.
More antennas means more range. The more devices you put on a router the less signal each one will start to get but signal fade only happens to cheaper routers with a bunch of clients. Even if you aren't going to be very far from the router it is still best to have the most you can get from the router due to any possible interference around. You want the fastest speed you can get for the money which is a given.