There is actually a handy diagram on pg. 10-1 of the 5145/55 operators manual that shows all of the grease fittings on the tractor (loader is not included). There are a few that you might not otherwise know are there, like the two rear axle carrier bearing fittings, and two under the floor mat for the pto and clutch shafts. I've greased mine a couple times since I've owned it.
I'm planning on doing the 50 hr. service myself, and I've got just over 31 hrs. on my 5155 now. I did all of the service on my previously owned 4540, including the 50 hr.. I'm with Andy in that I'm planning to just change the hydraulic fluid at the 50 hr. service. It's much easier to clean the strainer if you drain all of the hydraulic fluid first anyways. Other wise you'll just end up with 10 gal. of hydraulic fluid gushing out of the strainer housing while you're trying to remove, clean, and replace it. Been there with the 4540, it's not fun.
Another pro to changing the fluid is it's a good chance to replace it with a synthetic, winter-weight fluid if you live in colder climates. I can tell you from experience that "Mahindra" hydraulic fluid turns to extremely thick goo when the outdoor temp. drops past 25*F, and the pump really strains to push it until the fluid gets warmed up. Like, nails on a chalkboard straining. I actually used some high-dollar Liebherr fluid in my 4540 which worked really well, but I'm planning to try to same stuff that Andy uses this time around. I forget the name of it, he posted about it earlier in the thread.
Another thing to consider is changing type and viscosity of engine oil. Again, "Mahindra" 15W-40 engine oil is definitely not cold-weather friendly. I actually made a short video regarding the topic on my 4540, which I'll share if anybody is interested. Long story short, I highly recommend using synthetic oil if you live in a colder climate. I actually used 5W-40 synthetic in my 4540 which helped significantly with cold starts. Oddly, 5W-40 isn't on the recommended list of oil viscosities for the 5100 series, it calls for 10W-30 for cold weather operation. It's the same engine though, so honestly I'll probably use 5W-40 anyways since I've become a pretty big fan of it.