Consider tense (“time”) as just a small part of the verb system, Roland. Only the indicative has anything to do with “time.” Optatives, subjunctives, participles, infinitives, etc. have to do not with time, but with aspect of action progressive, aorist, or perfective. Those three aspects can be likened, as you suggest, to a movie, a snapshot, and a hologram respectively.
So a participle, if it is formed on the progressive (“present”) action stem, will express an ongoing action simultaneous with the action of the verb. However you choose to translate, your translation of the participle will always take that simultaneity into account: “taking,” “while taking,” “as she took/takes,” etc.
A participle formed on the aorist action stem expresses action that is already complete in relation to the action of the verb. Your translation of the participle will always take that completion into account: “having taken,” “after he takes/took,” “once/since he had taken,” “she (first) took it and (then)
Don’t be misled by English translations of the New Testament. For the most part, its Greek style is that of simple storytelling an intentional departure from formal Greek. This means that a “narrative” present tense (e.g., συνάγονται) will often be used where we would use a past. This does not affect the action-aspect of the participles. Υou are free to translate the passage you cite here any way you want, as long as you make it clear that the actions expressed by the participles are completed before the action of their verbs: “They came from Jerusalem and gathered,” “After coming from Jerusalem, they gather,” etc. The relationship of ἰδόντες to its verb ἐπερωτῶσιν (‘way down in verse 5) is the same: “Once they had seen
, they questioned,” “Having seen
, they question,” “They see
and they question,” etc. [That long parenthetical discourse running from verse 2 through verse 4 makes translation difficult, doesn’t it?]
You are quite right about the perfect and pluperfect indicative. As for the imperfect indicative, just keep in mind that it is a past tense formed on the progressive action stem; it expresses action that was ongoing or habitual in the past: “She was taking, kept taking, used to take, would take,” etc.