Keep in mind, anything you add adds to runout, how much depends on the quality of the parts and any adjustability you have in them. That's why set-tru type chucks are popular, you can dial them in to whatever you need. Better sellers will spec a runout level and stand by it.
I've only used a few LMS parts, but they have been good quality imports and shipping/customer service were top notch. I've never seen a setup like that MT3/3C converter, but I don't see any reason it wouldn't work.
One thing to keep in mind with collets, they have a maximum clamping range. ER40 is about 1mm (0.040"). 3C/5C tend to be lower, so you need to size your work to accommodate them or have a lot of collets. If you close them more than they are designed for, you can damage the collet and/or substantially increase runout. Same thing with trying to clamp even slightly oversize parts. This may not be an important issue for you, but it's something to make sure you know before you buy stuff.
I was going to find the range for the 3C, but my google-fu is failing me right this moment. Hopefully someone here knows off the top of their heads.
I've only used a few LMS parts, but they have been good quality imports and shipping/customer service were top notch. I've never seen a setup like that MT3/3C converter, but I don't see any reason it wouldn't work.
One thing to keep in mind with collets, they have a maximum clamping range. ER40 is about 1mm (0.040"). 3C/5C tend to be lower, so you need to size your work to accommodate them or have a lot of collets. If you close them more than they are designed for, you can damage the collet and/or substantially increase runout. Same thing with trying to clamp even slightly oversize parts. This may not be an important issue for you, but it's something to make sure you know before you buy stuff.
I was going to find the range for the 3C, but my google-fu is failing me right this moment. Hopefully someone here knows off the top of their heads.