It sounds like you have most things sorted. To convert an older mtb, I reckon on the following:

-change tyres to touring tyres (seems like you've done this)
-personally I'd keep the gearing (you've already changed this, but probably will not be a problem; you are usually better to run out of gears at the top end rather than at the low end when you need to go up a steep hill)
-swap a comfy saddle on (you've done this)
-put fenders on (you've done this)
-put a decent rear rack on (you've done this)
-change handlebars or gear shifting mechanism (not absolutely necessary, but personally I wouldn't want to tour for a long time on just a straight bar and you mention you have bar ends -I'd still consider the nashbar trekking bars though)

I don't know why you've been advised to change the front fork -perhaps because you might need front eyelets, but then again a pair or rear panniers and a front bag should be adequate. Other than that it may be for some other reason I've not heard of.

I tour on 1.25 slicks -some people think these are too harsh (can't say I notice in all honesty) but I'm not sure if thinner tyres will buy you that much more. I wouldn't think lighter wheels are going to be that much of a wise investment either -touring is about the journey, not getting to the destination asap -besides, generally speaking lighter can mean weaker, something that is a big no-no for touring.

The only thing from what you've said I'd place emphasis on is probably making sure you are comfortable; invest in a new stem/quill if you have to, change the bars to trekking or road if you really find those comfortable, put a saddle on you know you'll find comfortable.

if you're satisfied, then start looking past the bike to camping equipment and cycling equipment such as good gloves or helmet, etc.