1st trip that we're looking at is to Barcelona, end Oct/early Nov, and then from there maybe a couple of weeks later, over to UK for up to 14 days approx-best way to do this?
From Nijmegen to Barcelona you can actually travel with only two train changes (Amsterdam, Paris) & entire trip can be done within a day in case you go for high-speed trains (Thalys/TGV) option. However in terms of ticket fares it won't be very cheap even if you purchase in advance discounted train tickets, because Amsterdam to Paris it's at least 35 euro per passenger + another 100 euro for Paris to Barcelona leg. It is possible to make the journey much cheaper with extra train changes, but are you ready for these extra changes which mean longer travel time? On the contrary you can fly to Barcelona for about 20-60 euro from the nearby to Nijmegen airports (e.g. Transavia airlines from Eindhoven airport, RyanAir from Weeze airport, Transavia or Vueling from Amsterdam)
More or less the same story with Barcelona to UK (London). Here you can easily travel with only one train change in Paris, however again you should either go for expensive Barcelona-Paris train + not very cheap EuroStar train from Paris to London (from 51 euro) or agree to make extra train changes to make the journey cheaper. Airlines here harshly compete with each other, so air fare on route Barcelona to London is rather cheap, which means you can count on the ticket fare around 30-50 euro.
Next connection to be made is to get to Nuremberg from Arnhem/Nijmegen by 4pm on 11 Dec-what's the best way to make this connection?
Well, here probably train makes most sense. Although it will take you 6-7 hours and two/three train changes, but at least you can count on more or less good price (discounted tickets start from 39 euro, which isn't bad taking into consideration the distance). You can check timetables & purchase your tickets via German Railways (DB) website
(discounted tickets go on sale 92 days before the journey)
Then from there, looking into going from Vienna to Prague on 17 Dec-again, submissions welcomed on best way to do that, followed by next connection on around 20 Dec from Prague back to Netherlands-best way?
Again, for Vienna to Prague train is your choice (connections are frequent, journey takes only 4 hours and discounted tickets (from 29 euro) can be easily bought via Austrian Railways (OeBB) website
). Also here you can take a look at buses - rather comfortable (at least for 4:30-5 hour trip) & cheaper than train. With Prague to Nijmegen... well, by train the journey can be done in a day or overnight (in both cases changes required), while the best train ticket fare you can get here would be around 50 euro and it will require ticket purchase in advance. EasyJet airlines offer Prague-Amsterdam for Dec. 20 for only 45 euro, which ain't bad taking into consideration that it will be holiday time
Finally, going from Netherlands to Edinburgh to be there by 29 Dec, returning 2 Dec-any advice? Research so far indicates that air travel looks like best option-cost seems to be about the same as any of the other options, and a lot less connections/transitions to have to navigate...
Flying is rather convenient here since for instance already mentioned earlier EasyJet can get you from Amsterdam to Edinburgh for around 40-60 euro on Dec.27-28. However in case you really want to travel by land/sea, then you can count on some exotic options (e.g. DFDS ferry from Amsterdam to Newcastle & train to Edinburgh from there) or more trivial Nijmegen-Brussels-London-Edinburgh by train, which obviously will be more expensive compared to flying, however with in advanced bought discounted tickets the difference won't be super big
Also, have looked at whether a Eurail Pass would be worth looking at, and the conclusion that I've come to so far is probably not, but am open to advice on this too
Well, in case you ok with buying in advance discounted tickets (NB: some of them are nonexchangeable & nonrefundable), then pass is absolutely worthless thing here. Plus in your case many of the potential trains you would probably take will require extra supplements/seat reservations, which can be even more expensive than the ticket (e.g. Brussels/Paris-London) or cost the same as ticket (Thalys high-speed trains Amsterdam-Paris). Anyhow, thing like Eurail Pass is only makes sense in case you aren't sure about your itinerary until last moment and/or have no possibility to buy your point-to-point tickets in advance