Room for another opinion? You know, they're just like, ahemmm, we all got 'em
Concur with most of the previous posts.
Even tho theres nothing wrong w/the 54", if your layout allows it, go for the 60". It cuts down on your cutting turning radius, allows you to stay further away from the object your close trimming around and it cuts a bigger swath which cuts down on your mowing time.
Course the 54" has the same advantages over the 48" etc...
If space is a limitation, theres not a thing wrong w/the 54".
re FEL, besides the MMM, this is most important add-on implement you can have on a SCUT.
It'll carry things from point A to point B that'll save your back and do it quicker. It'll dig out most whatever you need to dig, it'll level terrain, with the addition of bucket hooks it'll lift things too big to fit in the bucket and on the BX series it can be mounted/dismounted in a few minutes without tools.
Theres other add-ons to the FEL such as a grapple or pallet forks that compeletely change it's function and usefulness too.
re. PHD. Theres many who use theres regularly so they're happy they purchased one and theres others that used it for a single project and it collects dust in a corner. You could always sell one after it's done it's job but I'd get an FEL over one personally.
re. grass catcher. I use a combination of gatorblades and a cyclone rake for clippings and leaf pickup. Upside is that it'll hold more than the OEM bagger and is easy on/easy off, VERY easy. Downside is it is LOUD, very LOUD and is another engine to maintain.
For grass clippings I mow in such a way so that I don't have the bagger mounted when mowing. I side discharge into several long windrows then go back and vaccum them up when I'm done mowing. Hook up to the cyclone rake is to back up to it, pin it on to the constantly mounted 3PH bracket, hookup the boot & hose then go for it. Takes a few minutes and is tool-less.
I great side benefit of bagging for me is compost, a fresh organic yearly supply of compost that so far has kept my small garden fertilizer free and feeds the Mrs' flowers.
Not to say that the way anyone else does it is wrong, as it isn't, this is just MHO and like evryone else, I got one too

Good luck in your quest....