I would appreciate any local knowledge or any previous knowledge in order to suggest any amendments to my routes.
And here's
my suggestion for a Day 2 route, based on yours (the implied philosophy thereof).
The hilly narrow road from N Tawton to Lapford is not fun: I have offered an alternative line.
From Nomansland (W of Tiverton) you're much better off staying on the B3137. Less climb (though it's mostly lovely descents) and you can use all that hard gained potential energy to maximum kinetic effect on the B road, as opposed to wasting it on heat (brakes) on the narrow roads your draft route took.
Out of Tiverton I'd take the Blundells Road to Halberton before cutting onto the canal path. This canal path is good, though care is needed under the frequent bridges (unclip and shout - I suppose a prudent citizen would dismount and walk each one).
From the effective end of the 'Western Union' canal path near Greenham, the NCN3 route is tortuous, slow and difficult to navigate. I have suggested you cut up through Wellington and put up with 3 miles between Wellington and Taunton on the A38 (only local traffic - the M5 takes the 'load').
To avoid riding through the confusing and often busy roads of Bridgwater, you can cross the canal before getting into town, but this does involve lifting the bike up and down a few steps to cross the foot bridge alongside the railway line to cross the canal. I found this not a problem with a lightly (6kg) loaded bike (but would be challenging with panniers).
The road due N from Woolavington to Bason Bridge and bearing round right to Mark is lovely and easy to navigate. You can then go through Wedmore but on
@Ian H 's 'Old Roads 300' audax a fortnight ago I chose to 'cut the corner' to the Cheddar road, and those roads were fine - exactly the route you had selected.
An easier route from Okehampton to Tiverton, as
@Ian H has said (a legend of unparalleled road knowledge btw), is via Bow, Copplestone, Crediton (hard hill over to) Bickleigh and these roads are all fine but I sense you want to plan to stay on minor roads if you can. I think doing 90-110 miles a day you will soon reassess your enthusiasm for this: they are slower, hillier, much more difficult to navigate, and if the narrow yellow ones on an OS 1:50000 series map, more risky/dangerous (imo) than an A road.
My Day2 route took a more northerly route than yours, heading straight for Taunton rather than going via Tiverton - see link for your interest, but look at the line from Axbridge north to inform your Day 3 (the line
@mjr has suggested).