Aside from talking to my chain of command and taking the DLAB test, what other steps do I need to take to reclassify in the National Guard?

35M requires a minimum ST score of 101, and a minimum DLAB of 95 (for the easy languages) and 110 for the toughest languages.
In the Guard, you typically reclass on your extension.
You can contract at 1 year out from your ETS, extending for a new MOS, new unit or both is called a Cross Unit Extension.

For what it's worth, 35Ps and 35Ns have more contracting job opportunities than 35Ms.

What SGM (Join to see) said about your GT and DLAB scores is correct. Though, the GT may be waiverable. At least, it used to be. As for the training, DLI will be heavily dependent on which language you get. I know for the CAT IV (the highest level) languages class is pretty challenging. Anticipate a great deal of homework if you land in one of the Arabic classes or the Chinese language classes. I had at least 3 hours of homework every night in Modern Standard Arabic. They used to offer study hall when I was there, but they were looking at stopping it due to lack of participation. If you go, and it’s offered, I highly recommend doing it. Any opportunity to study more is helpful. As for housing, they do have on post housing on Monterrey though that housing is primarily for cadre and people stationed there outside of student status. Fort Ord does have military housing and it’s not bad from what I a was told. The BAH is pretty high so if it’s just you and your spouse you could probably find a decent 1-2BR, 1BA apartment for around $1500 a month. It seems high but the cost of living there is wild. If you push out a little further (I lived in the outskirts of Salinas) the housing is more affordable though some parts of Salinas are quite sketchy. If you have any questions feel free to ask! I just retired out as an AD 35M.