I have a pair of questions about gaining momentum. First, do players gain momentum with bonus successes even when using momentum to increase the dice pool?

Second, if a player is assisting another player, would the assisting player be able to generate momentum?

I’ve checked the rule book for the answers but I haven’t found any. In the game I’m running I’ve been letting them go ahead and generate more momentum - how has everyone else been doing it?

You need to have Momentum available before the dice roll is made, if you want to buy additional dice.
Then you make the dice roll, determine the number of successes versus the Difficulty of the test, and any excess successes become (new) Momentum.
This Momentum can be used on Momentum spends for the currently resolved action or it could be stored in the Momentum pool.

Example:
Character A has to make a Difficulty 2 test.
The group Momentum pool has currently 2 Momentum.
Player of Character A decides to take 1 Momentum out of the group Momentum pool, to roll the test with 3d20 instead of the usual 2d20. The group Momentum pool now has 1 Momentum left.
The player rolls the dice.
The results are success, success, critical success for a total of 4 successes.
Compared to the Difficulty of 2, that results in 2 excess successes.
Those 2 successes become 2 Momentum.
If those 2 Momentum could be spent right away or stored in the group Momentum pool.
If they are stored, the group Momentum pool has now 3 Momentum left for the group to use later.

An assisting character does not generate any Momentum, but adds successes to the leading character for the action.
Those successes are added to give a total, provided the leading character has at least one success on their own roll, then the total number of successes is compared to the Difficulty of the test. Any exceeding successes become Momentum.

Example:
The test Difficulty is 2, so 2 successes are needed to succeed.
Charakter A is the lead, rolling 2d20 versus A’s Target Number, character B assists rolling only 1d20 versus B’s own Target Number.
A rolls 1 success.
B rolls a critical success on the single d20, adding 2 successes to the total.
The total number of successes is 3.
The Difficulty is 2.
That is 1 success exceeding the Difficulty, so this 1 surplus success becomes 1 Momentum.
This 1 Momentum could be spend right away or stored for later use in the Momentum pool up to the maximum of 6 Momentum.

Thanks. It looks like the answers to my question are yes and yes. The system itself is pretty easy to get, it just looked like these situations had fallen through the cracks in the book. Where did you get the information?

From the core rules. The description of those rules is not different to the rules for Momentum and Assist actions in most other 2d20-based RPGs. Those are some core principles that are not changed that much in each individual adaptation.
But, all 2d20 RPGs suffer from some unclear writing (some more so than others), so you need to read carefully, or ask on the forums or Discord or Reddit etc. for clarification.

When I read the ASSISTANCE rule, I don’t see any limitation on the creation of MOMENTUM. I do see that the GM can limit the number of PCs who assist, and that ASSISSTANCE is only allowed when/if the lead-PC scores one or more SUCCESSES. My preference is allow MOMENTUM to be generated both when it is used by a PC on a SKILLS-TEST, as well as when PCs assist each other. I believe the latter encourages role-play and team-work. If they are generating “too much” MOMENTUM, I can always just increase the DIFFICULTY. In the end, you are the GM, so you get to tweak the rules to suit your players and game. Don’t be boxed in by a book.

Re: generating too much momentum.

Momentum is capped at a party pool of 6 and at the end of each scene one momentum is lost.

If you think the players are generating too much momentum to easily you could restrict (or throw out) diff 0 rules.

I personally don’t like the idea/system of players choosing to roll d0 tasks for cheap and easy momentum (if there’s no ‘challenge’ you simply succeed). If they need the bonus dice there’s a shiny pile of chaos I’m sure they can ‘borrow’ .

As GM you can always disallow rolling D0 tests, if you think that an automatic success without any Momentum is fair enough for your players.
But, the players NEED Momentum, because you cannot substitute generating Chaos for all Momentum spends. So to create Truths and to make the Obtain Information spend, they need their Group Momentum pool and the individually generated Momentum points on their task rolls.

Buying Bonus d20s is only one of many ways to spend Momentum and it is one of the few that could be substituted by generating Chaos.

Guess it depends on your playstyle (as a traditional player dipping his toes into narrative elements of play).

By allowing d1 to be the default rating I consider there is still a lot of wiggle room there for generating momentum?

I do feel that I would prefer ‘create truth’ to be a feature of momentum in my game and not something to be overused or overplayed.

I confess to not really appreciating the whole ‘ask a question’ portion of spending momentum as yet. My players in games usually tend to form the initial enquiry to regard what they are trying to ‘glean’ and I tend to give them results based on how well they do (even if it’s more information then they were seeking). I get it in something as information/tech heavy as Star Trek… but Dishonored, not so much.

*Note to self: for ‘ask a question’ read ‘obtain addition information’ (it’s the use of ‘truths’ / new terminology that made that seem confusing).