Ditto what was said above, for sensible play there's very little reason to grind for mats. I think most of the complaints come from newbies who relog-grind Dav's Hope and similar because Youtube told them to and they didn't know any better, and from obsessive completionists who insist on fully G5 engineering every ship.
Now to get to the OPs question, the Long Range FSD is indeed probably the most broadly useful engineering mod in the game, so it's a great one to start with. Also pretty accessible, as all the materials are easy to get. Let's take a look at the blueprint:
https://inara.cz/galaxy-blueprint/2/
If you're starting from zero rep with the engineer, bringing enough materials for five rolls per level is probably safe. (You can bring less if you've already ranked up the blueprint with that engineer, because the lower tiers complete in fewer rolls.) So by my count, that's:
- 10 Atypical Disrupted Wake Echoes (G1 data)
- 5 Strange Wake Solutions (G3 data)
- 5 Eccentric Hyperspace Trajectories (G4 data)
- 5 Datamined Wake Exceptions (G5 data)
- 10 Chemical Processors (G2 manmade)
- 5 Chemical Distillery (G3 manmade)
- 5 Chemical Manipulators (G4 manmade)
- 5 Phosphorus (G1 raw)
- 5 Manganese (G2 raw)
- 5 Arsenic (G2 raw)
The data are easy to collect, because they're all in the group that comes from wake scans. Equip a wake scanner on a fast ship and hang out at a busy port or installation scanning high wake signals as NPCs jump out. You'll have the necessary scans in ten minutes.
The raw materials are also easy to obtain, although it will take longer since you'll have to visit multiple locations. Equip the surface probe launcher and an SRV. For each element, fly to a landable planet with volcanism that has the necessary element, or better yet a higher tier element in the same family (see here:
https://elite-dangerous.fandom.com/wiki/Material_Trader). Probe the planet, fly down to a geological site, and break off the various crystals to harvest elements. If you collected higher tier materials, head to a raw materials trader to trade down for the stuff you need. EDDB and Inara can help you find the planets and trader you need.
Finally the manufactured materials are the only ones here that are going to be dropped from combat. Not very efficiently though, since the chemical machinery family is mainly dropped by cargo ships, so you can't just hoover them up in a CZ. Good options would be: blow up some NPC traders (up to you to do this legally or not); find some High Grade Emission USSes and trade down the G5 materials for the stuff you need; or take missions that give the manipulators as rewards and trade the spares down for the processors/distilleries.
If you're starting from scratch this might be a couple play sessions worth of activity, just because you have to travel around and set up ships for very different activities. But long term it's not hard to keep a good stock on materials on hand. Two key tips: #1 - whenever you're flying around, scan any NPC ship that passes in front of you, before long you'll fill up on lower-tier emission data; #2 - after any combat, check the contact list for G3 or better materials and scoop them up. Just passively doing those two things will ensure you have a good stock of manufactured and data materials that you can trade for what you need when engineering something. You'll still need to hit up geo/bio surface sites periodically to get the raw materials, but again, if you make sure to always scoop up any Needle Crystal or Phloem Excretion you see, you'll build up a good supply of high-tier raw mats to trade down.
