SillyOldDuffer
Thats an impressive list of things to put in an ER collet. I have a brace of nice Albretch drill chucks to deal (more) quickly and easily with most of those. Tramming device (Burk Co-Ax knock off) goes in a direct spindle collet. Slitting saw arbor and fly-cutter are direct to spindle shanks. The idea of futzing about with a collet to hold drills almost makes my ears bleed. I have done it with oversize straight shank drills for one off "why did I agree to do this" types of job and hopefully won't be revisiting the experience.
The Stevenson blocks, spindexer and work holding in a lathe possibilities are the best arguments in favour of a comprehensive ER system. But my main lathe is native 5C spindle taper and I have full sets of 5C by 1/64" and 0.5 mm so ER has no attraction there. Obviously my spindexer, hex block and square block are 5C. All get regular use. Great thing about 5C is being able to get hex and square collets when needed.
To my mind, except a lever action closer on the lathe, popping a native arbor out of a spindle is always going to be faster and less hassle than mucking about with collets for everything. Been mimbling whether or not to fit my lever closer for ages!
One great thing about this hobby is that there are many ways of doing things with considerable overlap between methods. What you do is always constrained by what you have. Given most folks budgetary limitations the art is to get what you need now and for the foreseeable future without exhausting todays funding. No point in overspending on tool holding and tooling in early days leaving no money to get materials and actually use the stuff.
In retrospect I spent far too much far too early in anticipation of what I might need! When an absolute "must have now 'cos I shall surely need it" sits in a cupboard for 30 years before triumphantly emerging to save the day its possible the need was overstated! Hope is fading for some 40 year and counting cupboard queens. I shall use my Edgwick (Cincinnati copy) dividing head one day. I will, I will! Got the wide range plate set too, how cool is that!
Bargain prices tend to have undue influence on me too.
If I were to do it again starting now I would go with several end mill holders, a good keyless chuck, direct to spindle arbours for slitting saws and flycutter, possibly a direct to spindle collet for the tramming device and wiggler / edge-finder too. Actually I'd ditch the edge finder and buy a Huffam type wiggler, more spendy but they work properly, always. I'm unconvinced about collet blocks unless your mill is small. 5C spindexer and 5C mount chuck could cover all collet block duties for me. The blocks only tend to come out when I can't be bothered to fit the spindexer or when I have vice set ups going on at the same time. Clearly if you eventually do decide that an ER or whatever collet set is your future way forward then starting out with a collet set will probably be cheaper.
One place I would spend out on is a good machine vice. If the size is appropriate for your machine the Vertex VJ400 is a decent vice with much larger opening capacity than the normal 4" jaw vice. Spendy at £250 (ish) from Rotagrip but I'd find an ordinary vice limiting.
Clive