Likewise.
And all you need is a rather low level spell on you or around you to negate heat loss. Not an issue.
Avoiding storms while in the air AND have plenty of speed, not so hard. The only real issue is the same as in current reality, people saying to themselves that "-i´m sure it´s not such a bad [weather], i dont want to bother going around it/ wait it out on the groung" and end up in trouble because of it.
1k miles in a day wont be hard anyway. You can easily stretch the speed while in flight a good bit further upwards still.
You´re controlling the wind! It´s just as chaotic or not as the spellcaster wants it to be!
Combine it with the heat regulation spell to make a layer of "nicely temperated" and "still"(relative to the person) air around the flier and you´re fine on both accounts.
I´ll reply there as well...
To navigate via Roman roads, somewhere between 500-1000m is probably low enough with ease.
Roman roads stands out from other roads even NOW, with lots of large and small roads everywhere, in medieval times they should be extremely obvious.
And even today, with all the roads around, novice pilots still use roads to navigate at times, some get lost, but most dont, and they can do that from up to around 3000m high, depending on what kind of landmarks they´re using aside from the roads.
Learning the terrain and landmarks in a completely new region will be somewhat troublesome and time consuming, and trying to find a new place, regardless of maps and their quality will always be more or less chancy.
But overall, navigation by landmarks from the air will probably be much MORE reliable most of the time than trying to walk the same route, simply because from the air you can actually see far more landmarks to navigate by.
(and this comparison gets rather fun if you also throw in the more surprising examples of failing to navigate, like both the Japanese and the americans in WWII Pacific, where despite decent, good or even excellent training and using compass, good maps and even radio compass, pilots repeatedly managed to get so lost that they ended up trying to land on their enemies aircraft carriers, thinking it was their own)
Yes things will block light(trees surprisingly little though), but as long as you´re not trying to fly "low", you will still be seeing FAR more and further than if you were on the ground looking for the same light(s).
Nope. As long as you´re not flying on instruments alone(or mostly) its relatively "simple"(probably wrong word).
On the ground you can easily get lost, and because you´re close to the ground, it´s hard to see how you went wrong and often where you are. In the air, you can see VERY far, so even if you were driven off your course by many km, you´re still likely to find it once you realise you need to look for it, and if you´re observant, you will quickly notice any drifting long before it becomes problem.
If you´re doing navigation for a flight all manually, there´s quite a lot of things to take into account, so it IS easy to make mistakes, but it´s really quite simple and mechanical math, and if you do something wrong you will quickly have plenty of chance to notice in what direction you were wrong. If you make a big mistake navigating on the ground, you´re much more likely to not notice it until you´re totally and utterly lost as you probably wont be able to spot the landmarks you wanted to see.
It´s the reason aircraft started out being used as tools for recon after all...