Old PC`s and Mach3

[A_Camera]

Once confirmed if it is the pc's onboard LPT connection causing the missed steps then for a beginner would the UC100 be enough for me?
Or would the UC400 still be advised (I only be using 3 motors for a while as being a beginner) so the UC300 would be wasted on me to my understanding.

The UC100 is sort of a USB - parallel port interface with a built in motion controller. It will replace your parallel port directly and you can plug the DB25 directly into the BOB, between the PC and the CNC. It has the advantage of that it is boxed and 100% plug and play, just install the driver, plug the printer cable into the DB25 and the USB cable between the UC100 and the PC, and off you go. But... it is USB.

The UC400 in your case makes perfect sense. It provides better noise immunity and it has an extra parallel port, so you can have more inputs/outputs compared with the UC100. The only disadvantage I can see over the UC100 is that it is not boxed and needs an external power supply, but the advantages clearly overweights the disadvantages. In my opinion, it makes sense to get the UC400, but makes no sense to get the UC100. I honestly think the UC300ETH would be overkill for you (as it is for me as well) unless you have plans on extending your machine with loads of extra buttons and other bells and whistles. I have no use for the analogue inputs/outputs at all, since I control my VFD via Modbus, but even if I would have used 0-10V I'd prefer an external PWM board. If I buy a new controller I'll buy the UC400 also because it is easier to install than the UC300ETH and the layout is better designed.