Bridgeport Manual to CNC conversion...

[JAZZCNC]

The UC300 USB motion controller goes to 100kHz so that seems ok, I only suggest that one because I have used the smaller UC100 with total success and the price is pretty good too. However I do not know yet if that interfaces direct with the servo drive unit?

Well not really 100khz is still 400khz short of full speed/res. Or 1:5 multiplier so only getting 5th of resolution. Plus it's USB rather than ethernet so wouldn't be my first choice.
Really Ethernet Smooth stepper is what you want or feeling really flush then go for Cslabs Controller.

Would you go with 750W motors or smaller??

Probably 750W but really you should do some calcs to get better idea of size, inertia ratio etc. Like steppers Bigger isn't always better.

2:1 reduction for resolution & torque increase, more?

Again depends on other things like screw pitch and what kind of speed/res/torque your looking for. Thou 2:1 with 5 or 4mm pitch screw sounds about right. My Big Semco CNC Mill uses 5mm pitch with 2:1 ratio and 1.8Kw servo's but it Dwarfs BP.
Matt (kingcreaky) on the Forum used 750W servos with 2:1 ratio on BP Interact sized mill and was happy with them. (He's got a video some where on this site)

Servo drives seem to have lots of settings, what is used - speed & torque, positioning..... All new to me but i have the manual for the drives now.

If using Step Direction then you use Positioning. If using Analog +/-10v control then would use Speed. You'll be using Step & Dir so positioning.

Difference between Step/Dir and Analog is mostly how they are controlled and how the Closed loop works. With S/D the loop is closed only between drive and Motor. Analog the Loop is extended between Controller drive and Motor.
The result is that Analog feeds the Encoder position back to the controller, which it must do to work, which then checks this position with the commanded position and if wrong sends corrective signals.
The upshot is that the DRO's always display the actual position of the table, no matter if mach or controller as commanded this or you whind it there by hand. In affect works just like Manual DRO's.

Step/Dir on the other don't do this. It sends commanded position to the drives and takes it on faith that it arrived there. The drive then takes control of getting to commanded position and any corrections needed.
So the DRO's only show the commanded position and if it's wrong or if for instance something is loose you'll never know your out of position. Essentially works just like your steppers now with the exception the drive is checking the motor actually moved the distance told.

Bottom line is S/D is easier to setup. Analog gives more feed back but takes more setting up and tuning of drives.

See this video I made showing 1.8Kw servos controlled via Analog.