However, I am plotting a trip towards the North East to try and bag some of the Heaton based DMUs whilst also trying to clear up some of the LNER stuff I still need (have any withdrawals begun with these yet?). At the moment, I am considering York as I can make it work financially by going via Tamworth and I thought I may be able to break the day up with a trip to the NRM - do a good chunk of the Heaton based DMUs venture to York?
Pelaw between 16:00 and 18:00 would probably be a good idea, it's an island platform and will probably get you the vast majority of if not all of the Metro units that are in service that day, along with the odd Northern service.
For 142s out of Newcastle, the 17:23 Newcastle - Stockton is almost always a 142, and the 12:16 Newcastle - Carlisle always used to be a 142 but I think that one might now be a 156. 142s are indeed becoming rarer out of Newcastle, but I think they're still the primary traction on the Tees Valley line.
158s do have booked workings from Newcastle now, usually two of them will be in service per day and work Newcastle - Carlisle and Newcastle - Morpeth services. Most Northern services in the North East are worked by 156s now and whilst it is mainly the Heaton allocated units, Newton Heath 156s do sometimes appear too.
For spotting on the ECML, my recommendation would be Manors as it's got an island platform and the line speed is still fairly low (about 40 mph iirc).
For spotting in the Teesside area I'd recommend Thornaby or Eaglescliffe as both have island platforms, and the former will also allow you to see freights entering and exiting Tees Yard. Darlington also wouldn't be a bad place to spot either, there's a good spot at the south end of platforms 1 and 2 that'll let you see everything passing through the station, and with the exception of one LNER service in the morning, and a very small number of TPE services during the day, all passenger services that pass through Darlington also stop there.
Regarding ticketing, if you're just staying within Tyne & Wear I'd recommend a Nexus Day Rover, National Rail ticket offices don't sell them but you can buy them from a Metro TVM (on the machines as a Network One day rover) for £7.80, and that covers all of Metro, all buses within Tyne & Wear, Northern for Sunderland - Heworth - Newcastle - Dunston - Metrocentre - Blaydon, and the Shields Ferry between North Shields and South Shields. The Nexus Day Rover doesn't have any peak restrictions either so can be used all day. If you want to roam a larger part of the North East I'd recommend a Tyne & Tees Day Ranger, which for £24.40 (£15.45 with a railcard) and is valid from 09:00 on weekdays (and all day at weekends), here's the validity map for it (from railrover.org):
Alternatively, if you have a few days available and want to expand the area you're covering you can get a North East rover, the 4 in 8 day version costs £104.20 (£68.80 with a railcard), and the 7 day version costs £119.70 (£79 with a railcard), and covers Yorkshire in addition to the North East. Same peak restrictions as the Tyne & Tees Day Ranger, valid from 09:00 (all day at weekends). Here's the validity map for it (again from railrover.org):
I'm probably not as knowledgable as some posters here but I hope what I've posted is helpful