To me the starting point is boots and socks, without them your'r doomed! Then, get to know your feet, at what point are you likely to get blisters and so on, its really worth doing the homework. Better to learn early than to be crippled by pain and still 10 miles to go before your walk ends!
Then trousers, I made the mistake once of buying a pair that was narrowly cut at the knee. I had to stop using them because they rubbed my knees red raw! My present pair have a bit of give at the knee so no further problems. My next priority is comfortable underwear, I prefer cool synthetic and cut as ordinary briefs, some people like boxers but if neither are comfortable, or make you uncomfortably hot when you don't want to be hot, it can become really irritating.
'Easy' for me to stay dry at torso and head level, but 'downstairs' can be a bit tricky. I personally have now settled on a good pair of gaiters (worn underneath my trousers of course) and a rain skirt which I find very much to my liking. I also find the rain skirt is good for temperature fluctuations, not so easy on a stop/start rainy day, especially if its warm(ish) at the same time, not the best experience if your lumbered with faffy trousers. My skirt can be on or off in 10 seconds and I dont even have to stop walking either, or rucksack off, then rucksack back on again. What a time wasting chore!
Apart from a waterproof outer or a poncho, (I'm using a poncho more and more) so even less need for the rain skirt, there is so much torso choice I think you will have to experiment with this and that until you feel comfortable. I'm still experimenting, I still can't get it right, always feel that there must be that 'right' garment out there just for me, but I just cannot find it.