Ah, ignore the bit about the Normans...that just the bias of a Yorkshireman
I think its more a case of me advising you not to make certain glaring mistakes that I did, but what the hell.
For England:
The trend in Anglo-Saxon England was towards consolidation into larger kingdoms during the sixth and seventh centuries, but from the seventh century onwards the borders of each kingdom began to settle and didn't change really from this point until the arrival of the Danes jumpstarted the unification of England under the House of Wessex. I think this has as much to with the depelopment of a functioning church-governed bureaucracy as with an early regional identity (as Mercians or East Anglians) that made governance easier for the migrating royal courts of the time. As it became easier over time to raise larger numbers of thanes for the royal households and collect more freemen to serve in the fyrd it meant that it became harder for Anglo-Saxon kingdoms to conquer one another. The Danes on the other hand, often striking along or through border regions with relatively great speed and in great numbers, were able to sidestep this problem and this is why Anglo-Saxon Kings found it so difficult to counter these invasions without reform of their armies like that undertaken by King Alfred of Wessex. Therefore I'd say that any land grabs by Northumbrian Kings should be relatively close to whatever POD you decide upon. Northumbria would also benefit from some form of natural boundary to discourage attacks from Mercia, so perhaps expanding the kingdom south to the River Trent as I did in my TL might be a solution.
Depending upon your preferences then, you might wind up with three to five decent-sized kingdoms covering modern England and the Scottish lowlands by the time of the Danish invasions.This stronger Northumbria might initially collapse like in OTL but with a stronger, more established dynasty might be able to revive under a capable ruler, though that would leave Mercia or Wessex to spearhead the drive for unification. Alternatively Northumbria might weather the Danish attacks like Wessex, and between the two the invaders are slowly squeezed out of England entirely without leaving behind any identifiable Danelaw, which in the end would lead to a truely awesome showdown. Theres not much chance of making two separate English kingdoms work, so ultimately you'd have to pick a favourite and allow it to unify England.
For more specific advice upon religion you'd have to provide a POD however as during the reign of King Eadwine you'd be spreading Roman Catholicism to the River Forth, but the later you leave the POD then the more likely it becomes that Irish forms of christianity will be adopted instead. The real butterflies for christianity will involve Europe however, as depending on how well the Franks fare in your TL will affect the eventual English conversion efforts in German-speaking regions. I can't see any glaringly obvious reason for this not to take place, barring bouts of serious infighting within the Anglo-Saxon Kingdoms themselves, so depending upon your choices you could end up with an independent kingdom of Frisia, or an independent kingdom of Saxony, or both, or a complete failure to covert anybody along the coastline of the Germanic Ocean (the North Sea).
Scotland is unfortunaterly less of an area of expertise for me, but I'll do my best:
As I said before I can't see how you can really prevent the Picts from being absorbed into the wider Gaelic-speaking culture given the influence of the Irish church and the steady expansionism of the Dal Riatan Kings. Better kingship might see the Kingdom of Alba keep possession of or even regain some of its old holdings on the Ireland with an early POD and a channel-spanning Gaelic kingdom would be an interesting addition to a TL, though instability between the two halves of the kingdom might cause problems for even a string of decent kings.
Viking enclaves on the mainland of Scotland or Ireland and on the offshore islands around them are still likely to develop, but their success or failure ultimately depends upon the degree to which the Danes and Norse there become unified. Too little and eventually they will lose their holdings to renewed Scottisah and Irish attacks, but if its too much then its likely to take several centuries of effort for a developed Scandinavian presence to be fully reduced. I'd ultimately see the border with England settling along the River Forth, or perhaps a little further south to the northern banks of the River Clyde in the west if the Scots maintain control of modern-day Stirling.
With the Scottish lowlands in the hands of the English though, the kingdom of Alba isn't going to much more than an occasional nuisance unless it acts in conjunction with a rival kingdom to tackle Northumbria. Anything more specific upon the relations between the two kingdoms is again reliant upon you providing a POD though.
Thats enough of my rambling though. Have you got any thoughts upon what you want to do with a potential timeline? If so I can into far more detail than I have done if you need any help drawing it up.