INCOMING WALL OF TEXT I'M SO SORRY
To address your second point about being an Ace of all Trades - not really a possibility. Skill ramps don't last forever, they're only at their strongest in your first lifetime after you were at a high level.
- Case Study: Several Generations of Chefs
Life 1: You spend your life leveling cooking. You probably reach a high level, but not legendary (100), as the devs has stated it won't be possible to max out a skill in one lifetime. You character dies a celebrated chef, but not level 100.
Life 2 (a): You are reborn and continue practicing cooking. By the time of your death this time, you are much better than you were in life 1. You are possibly somewhere in the high 80s or 90s - very very small chance you will have maxed out the skill.
Life 2 (b): You decide to take a break from being a chef and decide to be a master thief instead. You practice your deviant skills, and reach somewhere close to sneak skills as you had in chef skills in Life 1.
Life 3 (a): You continue cooking. By the middle of your life, you are a legendary chef, master of all dishes, renowned across the lands. You're at skill level 100 and can concentrate on learning as many recipes as possible and making sweet sweet bank. You are at the pinnacle of your game.
Life 3 (b): You return to cooking, but because you skipped a lifetime of cooking, your skill ramp is quite small - you maybe learn your cooking skills a fraction faster than when you started. By the time you die, you are at a slightly higher skill than Life 1.
Hopefully this clarifies some things! Skill ramps apply for a limited number of lifetimes, and are at their most potent the lifetime directly after you get to a high level in a skill. There are two possible time lines here - (a) and (b). Neither is necessarily any better than the other! But in timeline a, by practicing cooking over several lifetimes, it is possible to become the best possible chef. Skipping even one lifetime and not really practicing sacrifices the skill ramp and leaves you almost back at square one.
So you can see, becoming a master of all skills will not be possible in CoE. There simply is not enough time in one life to level all skills to a high enough level to be able to have the necessary skill ramps to continue practicing in the next life.
However, because professions are not set in stone in CoE, unique combinations of skills to make unique professions are encouraged, and it will almost certainly be possible to master a few skills over a few lifetimes. For instance:
Legendary smithing and legendary artistic or filigree skills may make it possible for you to be a legendary maker of beautiful armors.
Legendary sneak and legendary one-handed may make you extremely adept at assassination.
Legendary beast taming combined with legendary farming may make you one of the greatest breeders around.
I truly hope this gives you a better understanding not only of skill ramps, but professions and skills in general.
TL;DR: Skill ramps carry over between lifetimes, but fade over time. Only by practicing the same skills on the same soul repeatedly will give you absolute Legendary (lvl 100) mastery of those skills. You won't be able to do this with all skills, but with dedication, maybe 2 or even 3.