For the FSD, if you go with the DBX don't forget to get a pre-engineered FSD, not the standard one. Adds quite a few LY. An all-out DBX can do 80+ LY.
This really depends on how much exploration you plan to do in this ship.
A standard engineered FSD can get a lightweight but not hyper-optimised DBX (i.e. no lightweight engineering on other components) to ~65 LY range without the Guardian booster. That's 16 jumps per 1000 LY.
Swapping for the pre-engineered one will get ~68 LY range on the same build, which means 15 jumps per 1000 LY.
So for every 1000 LY travelled, you save about 1 minute in travel time by using the pre-engineered drive. (If you're neutron-boosting heavily, this is 1 minute per 4000 LY instead)
But ... the pre-engineered drive costs about twice the materials of a maxed G5 standard FSD. You need to get 26 Tellurium and another 8-10 Datamined Wake Exceptions. That's going to take a while - probably an hour or two.
So you only come out ahead over the standard engineered drive after travelling probably around 100,000 LY (more, if you use neutron boosts). That's a long way - you could cross the galaxy and get most of the way back for that. Any time you spend jumping at less than max-range (because you're looking around near a nebula or similar) you get no benefit at all.
An interesting counter-proposition: only upgrade the drive to G4, plus the Mass Manager experimental. This gives the lightweight DBX a range of ~61 LY, which means 17 jumps per 1000 LY. So, that's a minute more per 1000 LY again ... but your material costs are massively down: you don't need any DWEs or Arsenic or Chemical Manipulators, it's all much more common stuff and less of it. So you save a couple more hours of material collection, in exchange for it taking a couple more hours to travel 100,000 LY. If you're "just" planning to wander around the various nebulae near the bubble, maybe hop over to Sag A* or Colonia as well ... you're probably going to be more efficient just using the G4 blueprint.
And you can go further: G3 with no experimental gets ~55 LY range, which is just over 18 jumps per 1000 LY, but basically no material collection requirements at all: you could get everything you needed by completing one decent mission to trade down for the Chemical items, scanning a few wakes at the engineer's base when you get there, and hopping briefly out in the SRV to shoot a rock or two for the Phosphorus. Compared with the pre-engineered drive, you've saved several hours of material collection, and it'll take you three minutes longer for every 1000 LY travelled (or 4000 LY if neutron boosting) - with a bit of neutron use, you could do an entire trip out to Beagle Point and back, detouring to various landmarks along the way, and still save time over getting the pre-engineered drive.
Calculations will vary depending on ship build. If you're planning to explore around the outer rim or a long way off the galactic plane, the diffeence between 61 LY and 68 LY may be the difference between being able to make a jump at all or not. But very often you don't need to maximise the ship before you set off - don't feel you have to! Most of my exploration was done in a Python with 20-30 LY range depending on how much engineering I'd had time for and what else I put on it: I've used faster ships since but once you get over about 50 LY range it really stops mattering much in most cases. Conversely, if you've been playing for ages and have near-full material reserves, sure, get the pre-engineered drive, you might as well. But don't automatically go for the "best" module: the time saved by using it might well be wiped out ten times over by the time needed to get it a lot of the time.