I think that's an impressive list for a newbie! However I agree with BG that you need more M2's! And a lot more M3's come to that.
The problem - or is that the beauty - of listening to and enjoying music, and maybe especially the music of Mahler, is that one person's super-dooper performance is another persons ho-hum. That's me with the M2's of Klemperer and Kaplan: they simply don't grab me.
I have a lot of digi-downloads mostly of live concerts (radio broadcasts), some of which are pretty awful, but some of which are superb such as the M2 by the Sao Paulo State SO under John Neschling; the 1975 Boulez Proms performance of M8, and the Marin Alsop / Bournemouth SO M3 from 2007.
I also have some oddities such as DLvDE sung in Chinese, and some non-commercial provincial releases such as M3 by the Slovenian Philharmonic Orchestra under Marko Letonja, and the same by the Scottish Sinfonia under Neil Mantle; an M2 by the Bristol Concert Orchestra under Stefan Hofkes from 2010 and an M1 by the Wiltshire Sinfonia under Malcolm Binney from 2008 (with a cracking 2nd movement).
Of the commercial recordings not yet mentioned, I particularly enjoy the following:
M1 - London Philharmonic / Delogu
M2 - CBSO / Rattle; Robert Schumann Philharmonie / Caetani (a bit ropey in places to be honest but with the very best of big finale endings, especially if you get the audio dvd version)
M3 - Sofia Philharmonic / Tabakov; Philharmonia / Zander (despite the posthorn being on the moon, but especially the manically fast end of the 1st movement!!)
M4 - Ljubljana / Nanut with Max Emmanuel Cencic, boy treble
M5 - I don't know this one so well, but the Symphonica of London / Wyn Morris recording is fantastic.
M6 - LSO / Levine
M7 - Yes, I like the ultra-slow Klemperer here (even though I don't like his M2's)
M8 - Warsaw forces / Wit
M9 - Klemperer again for me, New Philharmonia; but also the Rundfunk Sinfonieorchester Saarbrucken / Herbig
I don't know the 10 or DLvDE or the song cycles well enough to offer options, but I do have the Nagano DKL and it is superb!