Normal club route to Swain's Lane is along Pemberton Gardens and Bickerton Road, which is a nice warmup hill. Depending on how much traffic you fancy you might want to go through Finsbury Park (the park) in both directions and use Hanley Road / Marlborough Road to reach Holloway Road.
In Highgate you might as well start from the very end of Parkland Walk on Holmesdale Road nearer Highgate station, which definitely has a ramp (the entrance you've chosen might be steps, can't remember). Parkland Walk is unpaved so if it's been raining it'll be muddy, but probably traversable.
If you're going up Mott Street, you should continue to the High Beech tea hut for cheap coffee and Battenberg (keep going straight on at the crossroads, it's at the far end of the car park).
Other than that, looks pretty good.