As a proud ML owner they are a great unit for getting out and amongst it.
Regarding mods the best place to start is suspension, and in my experience don’t go a generic budget option to save a few hundred, I did at first and yes it was great on the paved stuff, but the teller for me was off road.
My mods to date with pricing as best as I can remember
Tough dog 2inch lift (foam cell) $2k fitted
Recovery kit $200ish (4x4 supacentre has deals all the time)
Under body protection was around $600 (had them fabricated, long story)
Tyres around $1500 (they have done close to 90k so it was a while ago) 265/70 fit without a lift
Uhf 200-700 all depends on what you want/need
Thoes are the basics to really get you out there in my opinion the limit is really on your budget
The one massive thing I will recommend is a MN centre console, I got sick of not having an arm rest, I picked up all 3 pieces for $120 and it fits straight in, took me 30mins to fit it.
Definitely put some photos up of your build, something I wish I had done.