Lens shade - your darkslide can double as a lens shade.
The Toyo loupe is money though. The best robust loupe you can get.
A lot of what you need for 35 mm photography is also needed for large format photography: lens cleaner/cloth, cable release, filters, etc. I think that you'll find yourself making exposures longer than one second. I find a digital wristwatch to be better than counting seconds in my head.
A small can of Dust-Off, small roll of white artist tape, a sharpie pen, ziploc baggies/Eagle Creek pack sacs to carry stuff.
Dust-Off? Don't use that stuff. The accelerate will screw up anything it touches. I use compressed CO_2.
Don't forget a bellows-factor gizmo. Mine is a day-glo, one-inch-long piece of alu tubing (to put in the scene) with the the bellows-factor scale (to put in the ground glass) rolled up inside.
I'd rather just measure and calculate.
Gepe makes nice cable releases.
Lens? There are lots of choices, pal. Tell us what you want to shoot and you'll be flooded with suggestions. A good "starter" lens for 4x5 might be a 162mm Wollensak Velostigmat series II, Kodak 203mm Ektar, Schneider Symmar convertable, just about any 210mmm, G-Clarons, Dagors---take your pick!
For ebay film holders, get good looking ones. Trashed out looking film holders are likely abused and have a better good chance of being leakers. You shouldn't want those. You don't want "tilt-all" film holders, either. Stick with Lisco, Fidelity, or the old Riteway Graphics. buy a stack of them or you'll get scr*w*d with the shipping charges if you win one or two at a time.
I steal time at 1/125th of a second, so I don't consider my photography to be Fine Art as much as it is petty larceny.
A black Levi's T-shirt, size L, has been my favorite darkcloth ever since I bought it in a sale some years ago. It cost me about $1.50...
The Tessar 150/4.5 has a slightly sticky shutter, but should be decent after a little exercise. It's just to get you started looking through the camera, really! And also so that you have a better chance of decifing what focal length might be worth looking for as a next lens - or maybe 150 is right, but you just need more movements?
The camera HAS built-in ground glass protection, so that's one thing less to worry about. But it makes some loupes more difficult to use without removing the plexiglass protector, so it might be an idea looking for one which doesn't have to sit flat on the GG to focus.
"Dark cloths aren't a problem if you have a sewer in your family"
Let's hope the OP has a seamstress in the family rather than a sewer!
"If you want nice fresh oats, you have to pay a fair price. If you can be satisfied with oats that have already been through the horse; that comes a little cheaper."