I have two thoughts on Catalogs.
First one is that by using the Catalog manager you risk corrupting the Master Catalog. It is a dialog box with many settings, screw up a couple and you screw up your catalog. So if you are going to go in there, make a back up first.
Second one is that you can add anything you want to the existing right catalog without risking 'screwing things up' to much. So I suggest using it.
I have a couple of thoughts on items that you want to add:
First one is that as far as I know, there is no way to select a bunch of 3DS files or folders and have them automatically be added to the proper 'groups' and then be filtered into the sub groups. For example you have a bed and it should go in Bedroom furniture within the Interior Furniture Group (if you want it that way).
Second aspect of items to add is that they require sizing and materials. Maybe most are sized correctly , maybe some have materials but many items can be sized to mutiple sizes and have multiple material options. There is nothing more frustrating than having sized and added materials that you like in one job , only to find it 'as default' in the next job.
Based on these observations what I've been doing is adding what I need to the right catalog.
You can right click in the Group area and 'add group' naming it Mikes Imported files or Mikes Beds or Mikes Interior Symbols. This can be done generically in an option like Interior Accessories or specific like 'Furniture'.
You then go down below where the list of your symbols are located / Right Click and select 'Add Element' / then select 'Import Geometry from file'. Locate the file you want to add, and if you want , size it and name it.
What I normally do now is add the particular object to the drawing area , this can be blank or a current project. I then go to 3D View and zoom in on the symbol. I check it for size and materials. Sometimes a do a quick render of it to see how it looks.
Here is where the materials option come in handy. If I have a material in the program I like, I set the object to that material. But if I must import a material, I switch to Paint Brush mode and add the new material. I do this the same way I do the objects. I first create a new Group 'Mikes Materials' and then down below(right click) select 'add material' , and here I use the 'use texture' option and navagate to the texture I have saved on my computer.
Now when the material is assigned to the new object I have one complete object , sized / assigned materials and named all added to my custom Group for quick future access.
There is one other command that comes in very handy. It is 'Save Element to Catalog' located in File / Catalogs.
Let me give you an example. I needed a black microwave that fit above a stove. Well they are not in the catalog. So what I did is size the base micro from the program to fit in width pulling the dimensions from Best Buys available microwaves. I then did a Google search for 'black microwaves' and hit the Image option. I found one micro wave company that had a black one and also had a front view of it's unit. I saved the image as a jpg to my computer. I opened it in my photo editor and cropped out some white edging and saved this back to my computer materials files list.
Now I clicked on the microwave that I had resized, in materials I selected the 'front' material option and then reassiged my new 'black microwave image' to it. I had to resize the image in TFPlan and had to move it up / dwn / left / right to get it perfectly aligned.
Then I renamed it 'Micro Jks Black 1'.
Then I used the Save Element to Catalog command, clicked on the micro , said yes when asked if I was sure and I now have it for use for other projects without disturbing what was there as default. I did the same with the white ovens from the program.
I guess what I'm saying is that just adding a symbol isn't enough. You must consider it's size / materials / name and location and ease of access.
I find using the right catalog and the save element option to be more forgiving / just as quick and allows me to actually look at my results before I move on to the next file.
Example of Micro and Oven attached.
ps I noticed I didn't have the oven door aligned correctly. I went back to the material and used the arrows to move it left and get it aligned. I then used the 'save element' option and it said I already had a file named the same , do I want to save a copy of it. I said yes and the program added a (1) after the name. I can now go back and delete the original or covert it to a 'gas' range top and have it as black gas range'.