The bridge is always the better option as with my foreign reg plate it freeObviously it's a unique situation but I'd have thought you should be OK, I imagine most people doing long-distance trips will leave Wednesday night/Thursday morning, then come back Sunday night.
Personally I hate that Staffs/Birmingham bit of the M6. You might want to consider the A50 (Stoke-Derby) then down the M1. Also consider going east of London on the M25 - you get a toll over the Dartford crossing but otherwise it's generally less stressful than Heathrow/Surrey IMO.
And be wary of the M20 being a Brexit lorry park - you really, really don't want to end up in the left lane coastbound J8-9, you end up trapped in a single lane at 30mph with all the trucks. It's better signed than it was, but even if you are in the right lanes it's still a long way at 50mph.
Also they've been closing the M2 on some weekends - you want to take a look at the Highways England map of what roadworks are happening when.
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