Jack of All Trades and Reliable Talent should work together.
This is also implied by the Proficiency Bonus rules (PHB, p. 173), which state:
Your proficiency bonus can't be added to a single die roll or other number more than once. (...) Occasionally, your proficiency bonus might be multiplied or divided (doubled or halved, for example) before you apply ...
No. The 1d4+1 roll to see how many turns time stop gives you is not an ability check, attack roll, or saving throw, and thus Bardic Inspiration cannot be applied to it. You can tell the roll is none of those things because it is not called any of those things, and also because ability checks, attack rolls, and saving throws all use d20's, not d4's.
Cutting Words modifies the d20 roll, and modifiers don't cancel critical hits
The steps for making an attack are described as follows (emphasis added):
Whether you're striking with a melee weapon, firing a weapon at range, or making an attack roll as part of a spell, an attack has a simple structure.
Choose a target. Pick a target within your ...
The rules use a certain pattern when discussing modifiers and Cutting Words adheres to that pattern. It is therefore a modifier to a roll result and does not replace the result.
Almost without fail:
If a modifier is a fixed value, the rules use the words "modifier" and "penalty."
See Raise Dead, Resurrection, Slow, Alter Self, Haste, Magic Weapon, ...
Cutting Words is not a bonus or modifier, it is subtraction from a roll
This is unique language. In 5e subtract is only ever used in the normal English sense, it is never used to refer to the game terms "bonus" or "modifier".
For example, when explaining passive disadvantage:
For disadvantage, subtract 5
When explaining ability modifiers:
It is up to the DM, though seems unlikely.
Motivational Speech does not say in its description that it is a performance. This means it does not fulfill the requirements to perform for a minute in order to use Enthralling Performance. If the DM were to rule that it does count as a performance then the rules on casting come into play.
To cast Motivational ...