My advice is (Presented in the approximate order I'd acquire them if starting from scratch),
- get a good quality vise , drill chuck and collets (just saw the 40 taper, I'd focus one one ER collet holder/set and then end mill holders, you can work a 40 more than an R8 so end mill holders become more important) That'll cover 98% of it.
- Parallels, cheap are ok, its milling not grinding and if they're within a thou its good enough imo.
- Strap clamps, cheap is ok.
- Cheap square and hex 5c collet blocks. Super handy and low cost! (makes the most sense if you have good 5C collets for a lathe)
- Rotary table: buy a quality brand used. CNC has rendered them about obsolete in many commercial shops so there are usually some kicking about. Go the largest diameter you can (or can lift), 12" is my preference....else there is never enough room to mount things.
- Next, one shot oiler. Cheap oiler with good meters. Let stop wear before it starts!
- Angle plates of various sizes. Keep an eye out for a large ones, they come up used and are expensive new. V blocks. Cheap is likely ok for each, I prefer better stuff bought used.
- dividing head. Some RTs can be mounted vertically, but imo if you get a big enough RT, you can end up with clearance issues. I think DH bearing arrangements are better suited to the job job than an RT in the vertical position and they can also be tilted. Use quality would be my preference.
- Start collecting endmill holders. End mills pull out of collets in more extreme situations. Wrecked a part just two weeks ago...1/2" em @3000 pulled out. Grrrr....stupid me, I know better.
- A DRO is last on my list, (and many would argue with me on that placement). My rational is they are super convenient but doesn't really create new capabilities. Well, accuracy over a distance is one, but that is a) rarely needed and b) can be done other ways. Don't get me wrong, I love my DRO, but imo it makes sense to first acquire stuff that increases capabilities. IF you were buying everything all once, the yes, a DRO would be on my list.