First of all - I don't think it will be a disaster if we don't qualify for the C.L - long term it may actually be good because it will allow us to play a lot of youngsters, which we can't do against much tougher opposition in the C.L
But - it's impossible to predict who has the tougher fixtures.
If I was to give my thoughts:
United:
We have Chelsea, West Ham, Cardiff and City at home - 2 of those matches we should win, one we can win on a good day, and one will be really difficult. If we can get more than 7 points we have done fairly well
Everton, Wolves and Huddersfield away - the advantage here is that neither team will have very much to play for. Huddersfield is already relegated. So the goal imo is to get 7 Points. But they key is Wolves.
If we get 14 Points - that might be enough to secure top-4. If we get 16 we should manage top-4.
So United should end with 73-76 points
Arsenal:
Perhaps the team that is hardest to determine. Their home-matches on paper look fairly easy (Brighton, Palace and Newcastle), but they have 5 away-matches and some of them look tricky. Everton, Watford, Wolves, Leicester and Burnley. All those 5 matches are matches that Arsenal can win on a good day, all 5 are matches where they can drop Points on an average day.
I would still claim on paper that Arsenal have the easiest fixtures and I can't see Arsenal dropping much more than 6-8 Points from their remaining matches.
My guess is Arsenal get 75-78 Points
Chelsea:
Easiest home-matches, really tough away-games especially with their current form away from Stamford Bridge. Key for Chelsea is Cardiff - if they don't win today, I can't see Chelsea making top-4. They have Liverpool, United and Leicester away. I think Chelsea will get 10-12 Points at home, but it will surprise me if they get more than 6 points away from home.
So my guess is Chelsea will get 72-75 Points.
Spurs:
They have 2 away games against Liverpool and Chelsea where just a single point will be a big surprise. The remaining 6 games are all perfectly possible to win - but realistically they probably can only afford to drop points in 1 other game. So if Spurs win their remaining homegames (Palace, Huddersfield, Everton, Brighton, West Ham) - they will with 90% certainty be top-4 especially as they have points in hand
Spurs to get 75-78