How to choose step up transformers?

@lalitk : Yes, I am critical of most of the claims made for today's Hi End gear! But I am content to live with and use some of the best tube and SS gear of the pre- '90 eras! Three roomfulls, in fact! Plus many TTs and boxes of LPs. And not to forget the three RTR's and boxes of RTR tapes!

I have been using Grado MI's and various MC cartridges since 1976 - so I certainly have experience to draw upon!

Not sure if using a low-end MC is worth all the connections and lossy wiring over a good MM. Especially in your setup. Compare an Audio Technica VM760 with the MC configuration. 

I agree with the Audio Technica VM760 - that is one fantastic cartridge!   

GTE, it is basically a matter of impedance. If you buy a transformer matched to low impedance cartridges you should stay with low impedance cartridges. Same for higher impedance cartridges. I think you will find this very helpful https://www.sowter.co.uk/phono-cartridge-transformers.php.
If you know someone who is experienced with a soldering iron you get the appropriate transformer from Sowter, a british company who makes excellent products, and you have him mount it inside your Luxkit. They are quite small. Then you do not have to worry about interconnects. The transformers are around $100. Even if you do not want to do it that way visit the site as it is very instructive in lay terms.
I have put their transformers in several preamps including my own Conrad Johnson with great success.