You only need to patch the client, as all this does is managing how things are load and displayed.
For communication it just requests more chunks if you want to display more, there is nothing that needs to be changed server side to accomplish that. So, there is no need to patch the server.
Applied Energistics is a very complex mod. To put it into perspective, Direwolf20's mod spotlight on it totals one hour.
The concept of Applied Energistics is all about storing items as data on a disk. This allows one to create very compact storage rooms, that often resemble a server room (since, at the core, an Applied Energistics storage room is a server room).
AE storage is most commonly accessed from an Access Terminal, which will display all of the items in the system on a single, searchable page. In other words, it will sort everything on its own, appear in one location, and display an absolute count of items.
Items are stored on ME storage disks, which can be accessed from a ME Chest or a ME Drive, in conjunction with a ME Controller and a ME Access Terminal.
But wait, there's more: AE also adds a multiblock auto-crafting system, which you can add to your storage system. This will allow you to request that the system craft a piston for you, for example. It's also Ore Dictionary aware, so even if you don't have the correct wood planks, it will still craft.
The downside is that an AE storage system requires power (which makes sense; you can't access a server if the power's out). It will take either Buildcraft MJ or Industrialcraft EU, which is connected directly to your ME Chests or to a ME Controller, if you have a connected system. The power requirement depends on how many components are connected, and will be subject to rebalancing.
AE also adds its own quartz, which will only spawn in new chunks. This quartz is the fundamental material used in the mod.
Again, the details of this mod are extremely complex. But it's a very powerful mod, and there are many more possibilities than just "storage and crafting".
Best Answer
It depends.
If you have a lot of the same stuff (cobblestone, dirt, etc.) an Extradimensional Barrel is great (you can connect it to the AE system with a storage bus), but when you have a lot of different stuff the AE drive rules (8 drives with up to 64 types in each).