And again about modules for multitool (No Man's Sky)

Greetings, I already had a similar topic, but decided to create a new one anyway :) I
started playing sky on Xbox. A lot of incomprehensible in the game.

1_Question one: I bought a multitool at the station, chose the item not to change, but to buy and add something like that to the collection. As a result, my people are walking with a new MT and I can't figure out where and how to get the old one so that the modules can be disassembled at least. Tell me where.

2_Question two: there is such a modification for a multitool - a plasmancer, and there are all sorts of improvements for it, such as a decrease in the recoil of the plasmancer or an acceleration in the recharge of the plasmancer. That is, clearly related to the plasma launcher.
I have no modifications to the plasma launcher. But I found the Impulse Rapid Fire modification somewhere and installed it. It turns out that modifiers for a plasma launcher are suitable for improvement, or somewhere there are modifiers specifically for a pulse rate of fire?

3_ Question three: do bonuses from the same modifications stack, for example, acceleration of reloading if I put two modules, then the bonus is summed up?
sorry if the questions seemed stupid to you :)