Sorry to hear about this. I'm a scout leader and I'm looking for some large rucksacks and stoves. I'd be happy to give you a donation for most stuff as countless kids will be able to make very good use of it for years to come. My personal mail is open if you'd be happy to give us a look at it.
Snowdon to Foel Fras is has the advantage of being negiotiable in the dark as adequate knowledge of the Carneddau coupled with a GPS, map and compass should be enough to get you from from peak to peak and then follow the wall down to Bwlch y Ddeufaen (if that's where you're heading) even in a complete white out.
Foel Fras starts well but culminates in the biggest climb of the day when legs have already done most of the work. It took me 3.5 hours to gain Crib Goch from the Llanberis Pass - normally it's just over an hour. As a result we just got off CG as the last of the daylight went. Unfortunately this meant that we had to drop on to the Pyg Track and regain height via the zig zags instead of climbing Crib y Ddysgl in the dark - which in my opinion would be very unwise especially when tired.
Personally I loved going down the scree on Bristly, I hated going up it the other way round. Of course which ever you do there's there counter arguement on the lower slopes of Glyder Fawr.
Which ever way you go for it, consider booking the bunkhouse at Gwastadnant. It's bang on course and provides an ideal location to collect/drop gear and refresh.
If you go S-N, consider starting at Pen-y-Pas, gain crib Crib Goch, Carnedd Ugain, then Snowdon. Descend Llanberis Path to SH609559 and then follow Afon Cwm Glas Bach into Llanberis pass. You'll cut off a big corner and if you've booked the bunkhouse you can call in for breakfast.
I've used standard Staedtler highlighter pens on my 25k "Active" maps and then layed sellotape over the top of them. I've used this technique on many an occasion and not had a problem. If it's wet the map can still be placed in a map case but, even when out for turning pages, it won't come to any harm. After use the tape lifts and often takes the highlighter ink with it. More stubborn marks are removed with soap and water.
I teach the practice to my charges before setting them off on their own. By having the route "indelibly" marked it stops any arguments about what route should be taken and gives undisputable evidence about whether they are on it or not. More so it gives confidence and is one less thing for the group to worry about. On planned but unfamiliar I can't imagine why any one wouldn't want to mark up.
Experienced map-readers will cope with a pristine map, novices need as much help as possible especially when confronted with the numerous hazards that a day out can throw at them. Remember, it doesn't take much for a competent person to "lose it" in a tight situation. Something as simple as a marked map may get the group back to base much sooner than a rescue team could and so a lot of misery would be spared.