John Neal has a nice sample set of broad edge nibs.
N207. Broad Edge Nib Sampler
This sampler contains broad edge nibs from of all the major brands. This allows you to find which nib works best for you.
Sampler contains one each:
Hiro Tape 1.5mm & 3mm
Brause Bandzug 1.5mm & 3mm
Mitchell Roundhand sizes 1 (3mm) & 3 (1.4mm), plus one reservoir
Speedball C Series sizes C2 (3mm) & C4 (1.5mm)
Tachikawa 3.0mm
Many people agree that the smaller sizes of Speedballs are not advisable because you do not get very crisp strokes - so I would not recommend a set of Speedballs which is what you will probably find at a craft store. The nibs you have to order online will be so much better - assuming you do not have a broad edge supply store locally.
Mitchell's are nice because you can sharpen them, but you have to learn how to adjust the reservoir. Not sure if there are videos - if time permits, I'll look.
It is highly advisable to choose a holder that does not have the hourglass shape because the hourglass shape forces your fingers into one position and you might want to adjust your grip - which is easier with a straight holder.
There are several options of straight holders from John Neal.
Ink - once again - you can't go wrong with walnut ink. I hesitate to recommend a black ink - but I have noticed that when people who start with Higgins Eternal try something else - they are usually pleased - so I do not recommend HE as the first bottle of ink. While I love McCaffrey's for pointed nibs, it does not perform well for me in broad edge nibs. Moon Palace Sumi is popular and a good choice. My favorite is stick ink, but I would not recommend that for beginners. If you have already figured out how to use gouache for writing with pointed nibs and like it - you will probably love it with broad edge.
Paper - for me, broad edge is a little more forgiving than pointed nibs - 5-Star (or Mead) notebook paper is fine and really inexpensive. If you can afford the practice pads from John Neal, that paper is very nice. He has a grid paper. The copperplate slant lines don't work with broad edge styles - too much slant. Rhodia is nice.
Of course, a parallel pen (or a whole set) is pretty dreamy for learning broad edge. The ink that comes with the pens is bleedy - so you need good paper for practice. Parallel pens like walnut ink.
Hopefully there will be additions to this thread. I'm a minimalist - and honed in on supplies that work for me - and don't do much experimenting.
If you can afford Sheila Waters book - Foundations of Calligraphy - it's not exactly a *supply* - but it is a wealth of information on all the basic broad edge styles.