Well I use LR as my go to image management system, so I made a bit of an effort to make it work for me. Firstly I would definitely keep with the one catalogue, especially if you ever need to find images from more than one shoot at a time, and this can include simple things like sending a print job to the lab.
Once you are in the LR library you have many ways of managing your images,on the file system and with collections and smart collections are probably the two easiest ways. I tend to not bother that much with the file system, since this way you can only sort the images by which ever folder you chose to place the image in. So I have a master folder for each year, and then images get put in folders by date. Probably the most simple solution after just folders by date, since you cannot really count all images in the same folder as organisation.
What I do do though is keyword all my images, and also apply IPTC Subject Codes, this makes sorting images very easy. I then use collection sets and mostly smart collections to organise the images. This ends up looking much like a folder tree structure, the smart collections look at things like particular keywords and IPTC codes, as well as other added metadata such as star ratings and labels to select the images to show in the collection. The great thing about collections is that a single instance of an image can appear in multiple collections. This is a great way to get round the multiple categories problem that doing similar sorting using the file system causes.
Your choices for working with collections allows you to use just about any bit of information relating to the image as a sort option. Or you can just use a standard collection, and add images to it manually. The great thing about smart collections is that they sort from all of the images in the catalogue, regardless of location in the file system. Although location in the file system is one of the sort criterion.
This is how I do my LR catalogue, and I also now only have the one, when I started I had a couple for different projects, but it got to be a PITA having to close LR to open a different catalogue, because the image was in the wrong one when I needed it. At the time I felt I had a good reason to do this, but I soon realised the error of my ways. I think back in the days of LR 1 and LR2, large catalogues caused some performance issues, but that was sorted in LR3, so that now catalogue size doesn't really play a part in LR's performance issues.
Alan