Be forewarned about trying to go fast on byways.
I'm the first in line to both congratulate and encourage you... but I am very much a 'you gotta learn to go slow' kind of byway rider.
At the moment the weather is rubbish and the lanes will become incredibly muddy and slippery. That's fun, but comes with its own risks. The empty lanes mean you haven't yet learned to deal with the other byway users.
Your top three are horses, doggos, and walkers. MTB guys won't hear you beep or rev, and other bikers and quads may struggle as much as you to choose the right line for you to pass each other safely.
Horses, you stop dead as soon as you clock them, engine off, get out the way. You need to learn how to grab a fistful of front brake, hit the killswitch, and then pull the clutch to allow the last of the momentum to roll you calmly onto the verge. If there's enough space and time then great, use the engine to rev out the way, but you're safer killing it and rolling to a stop to the side.
People also say carry mints for the horses. Me personally, I just try to keep out of the way of a panicked sideways equine dropkick.
Dogs will forever be off their leads. Technically a byway is an unpaved road so they should be under control (on a leash) at all times. Half the owers won't even realise you are allowed to be where you are. I try to give a bi-beep of the horn from a hundred yards, slow down, take a side, and idle the engine. If there's multiple dogs or one cowers, engine off. If it's a gun dog, it'll walk past you looking for game.
Ramblers/walkers will be the pits. You'll get the number of them happy to wave as you wave, that appreciate the bi-beep warning and shout of hello. What you will remember all week though is the one that gives you a shout and nasty words because they have a National Trust sticker on their windscreen and that means they can police the lanes.
40mph is fast. It's not excessive, but it's fast. My slam was 30mph and usually I'm not going over 35. I have hit maybe 50 or so on gravel and hard packed stuff but it's just not worth it. You want momentum not speed.
All this as TL:DR as it is, get out and do the drills. Get used to stopping before you are stopped by something. I enjoy the drills, because practicing dead slow stuff and braking on different surfaces means confidence in any scenario.
You'll feel a lot of difference with the front when your position is good and far back on the seat when standing. All the weight off the front keeps the wheel light and suspension un-loaded so it glances over rather than slamming through obstacles. Then try leaning forward and you'll notice the change. There are benefits to both depending on the terrain and speed.
Oh also double check your lever position for your height and riding position. Mine are pretty parallel to the ground, to force me back on the seat. No bent wrist when on the brakes, and no leaning forward when arms and hand are straight and locked.