I'm based near Edinburgh, but am occasionally in various corners of the country, and if I happened to be near wherever you are, I'd be happy to pop in for an hour or so.

There is one main standard for lathe tool holders, however there are also some manufacturer specific types, but they tend to use non-standard codes.
The key bit of info are the letters, as they tell you the insert type, toolholder style, and orientation. The numbers that follow are the shank size. Then the final code is the insert tolerance/size.

A SDNCN 1212 M11 takes a DCMT 11T3 insert
The SDJCL/R are left and right versions of the same tool, however the left hand version takes a DCMT 11T3 insert, whereas the right hand takes a smaller DCMT 0902, however 0902 is not a common size, so you'd be better to buy a new holder.
www.shop-apt.co.uk is a reasonable source for tools and inserts.

What I meant by tools lining up, is provided the tool disc/holder and the ratchet has been machined correctly, once you have one tool at the correct height, they should all be at the correct height when in the cutting position. If you're having to adjust the height of individual tools, then something is not right.
When I bolt a tool into my turret, I don't have to adjust it's height. If the height is wrong, then I have an alignment issue and all the tool heights are wrong.

If homing is working with suitable switches, when you click the Home (I think, it's been that long since I've used Mach 3, it might actually be Set Home) button for the axis, the corresponding axis should then carry out a homing routine.