Well I feel much the same as circlip too.
Once you have a vice , it only takes an ordinary bolt and a file to get it held down – at which point you can make tee bolt heads by the mile.
A length of your chosen metric studding, some hexagon for coupling nuts, and some bars with holes drilled in them (later to have slots added) and you have a hold down kit for pennies.
You need a decent setsquare – one that will go right across your milling table, for setting most things square.
Angle plates – the other route is to buy the rough castings and machine them. Hermingway do them I think.
Cutters depends on what size you are playing with. I do all my facing and profiling with 2 endmills. (You don’t need a set of endmills) A 2″ tipped cutter, or a 16mm tipped cutter. Slotting I use FC3 throwawys in a holder T built myself. They double as slot and end mills in hte small sizes
A slitting saw arbor you make – buy a couple or 3 2MT soft blanks. the driving peg you add makes htem much more efficient.
Parallels you make mostly, until you can afford a good set of your own.
I must say I like steam edgefinders and wobblers. Even more since I got a DRO. I have a laser edge finder that is very quick and easy, but its not as accurate as an ordinary over centre edge finder.
Boring head. In theory very nice. How often do you actually use one.
I used one once on the lathe before I had a mill to do the cylingers of a Stuart Launch.
It can be used for offestting tapers without moving the tailstock – good idea but I built a taper turning attachment.(not used much but a life saver when you do want one)
I used it once to bore the smokebox of the TE, and for the remainder of the 20 years I have had it, its gathered dust.
A boring head is one of those things that waits for a job that needs one.- unless you like a VERY EXPENSIVE flycutting head.
You MUST have some sort of dividing gear. (Unless you have a DRO for your mill )If you have a Myford, you build a GHT VDH dividing head.Of course it can be done by stepping out with dividers, but to make a cylinder cover and cylinder with studs to match, without a DH is painful. Or any kind of slotting on shafts which have been turned and are left in a chuck, or to make your own boring bars etc etc. Start with the simple kit, and add the goodies later, but you will need as an essential, a dividing head, and a set of raising blocks with a built in aligning tenon if you are going to make a steam engine on a mill. Hemingway again, – but I think I got my castings from Reeves many years ago, so they may still do them.