If you use no filter at all with multi-grade papers, you get much shorter exposure time and equivalent of grade 2 contrast, which is considered "normal" contrast. I do most of my printing with grade 2 to 2.5.
The Ilford under-the-lens kit comes with a bracket. You have an option of using 3 bolts that comes with it to clamp onto the barrel of the lens OR use a thin metal frame with 3 prongs that goes between the lens and the lens board and hang the bracket under the lens. Basically, Ilford gives you two option to mount the bracket to hold the filter under the lens.
I used some metal bracket purchased from home improvement center to mount this bracket little more permanently. Once you get a set, you can figure out how it best goes onto your enlarger.
I'd say start printing with out the filter but order a kit so you'll have more options.
Enjoy your new enlarger!