First, you are looking at a big tractor for 5 acres. Or is it 5 acres that you mow and there is more property to maintain?
Regarding MMM, those are almost brand specific, meaning there are SOME aftermarket units, but they are typically hard to find. MMM are expensive, but are nice for mowing. You will find one long thread about a NH TC24D with a MMM (rear discharge version) that causes clumping of the grass when it is wet or long. Some people on that thread don't have a problem. Side discharge does not seem to pose any problem with clumping. I use a rear mounted 60" Befco rear discharge finish mower and see some clumping so I wonder if the rear discharge units are all similar with that problem???
Regarding R4 tires, those should not pose any problems for you with the mower deck on either tractor. R4s are nice, I have them on 2 of my tractors and they are reasonably good on the lawn unless the lawn is wet then you might see some tearing. But it is a good compramise tire that will give you reasonable traction when using the FEL and still not tear up the lawn when mowing.
Regarding your choice of tractor brands, I have a Kubota B2910 and a NH TC24D. Both have hydrostatic transmissions. I believe the NH is currently the better value offering a slightly better design and slightly better tractor for the money. But 2 years ago when I got the Kubota I would have said the same thing about that brand. I like both, you'd be happy with either, but I question your need for such a large unit for mowing 5 acers. I could not go back to mowing with the larger 30 hp Kubota after using the smaller 24hp NH. The slightly smaller NH units turns much tighter and is much easier to get up close to fences, trees, the house, etc. I still use (actually my wife does) a Cub Cadet garden tractor for getting up next to the house, porch, etc. But the large frame Kubota is like steering a school bus around the yard in comparision to the smaller New Holland.
As for the things like the tiller, phd and snowblower . . . all are available from many sources and all are interchangable as long as they are made for a standard 540 pto and a standard 3pt hitch. NH also has a front mount blower, but that is a NH specific piece, you don't find too many front mount blowers.
As for prices, I think right now NH offeres better prices on tractors. At least they do in my area. As for prices and selection on attachements you will find a WIDE varience in quality and prices on each you look at. Woods and Land Pride are typically on the upper end of the price spectrum and are very high quality. Midwest (available under their own name and one or two private lables such as Corriher) seems to be in the middle and from my personal experience seems to have very high quality. Howse, King Kutter and a few more are on the bottom end of the price ladder and are often lighter built, but still offer a lot for the money.
Consider how much you will use an implement before spending the money. A PHD might be used a lot for 1 summer and then very infrequently after that, you might want to pick a lower priced brand for something like that. A mower will probably be used weekly for many many years, so opt for a sturdy unit with good design. Tillers are mostly foreign made, some have 4 tines others 6, some have gear drive others chain, but how big of a garden do you want and what plans do you have may determine the features you want.