There are often questions about the long list of dependencies in this mod. In general, for the full effect of this mod, all required mods are strictly required. However, if you don't want to use this mod to the full effect, some required mods can be relaxed.

1. Community Highlander - obviously necessary, and you should use it even if you don't want to use this mod.
2. Community Promotion Screen - necessary to properly display four rows of abilities. In theory New Promotion Screen by Default also works, but Community Promotion Screen is just strictly better. If you use RPGO, then you can ignore this required mod, as RPGO has a built-in version of New Promotion Screen by Default.
3. Proficiency Class Pack - required. Many classes have abilities from the proficiency classes. Without this mod, they won't have these abilities. If you do not want to use the Proficiency classes themselves, then you may use Disable Any Class mod to disable any class you don't want your soldiers to use.
4. Combat Engineer - same as 3. Technically, the only ability used from Combat Engineer is on the Pioneer spark. So if you don't want to use the Pioneer spark ever, then you can ignore this mod.
5. Proficiency Skirmisher and Reaper - Some abilities from these mods are used here. However, this is slightly different than item 3. Proficiency Reaper and Skirmishers are reworks of the basic classes, and not new classes, so you can't disable them with that mod. If you don't want to use the Proficiency version of the Skirmisher and Reaper, go to their mod folders, and delete XComClassData.ini files.
(note that I did not test if there are any other changes required to make sure you won't see the effects of the Proficiency faction classes).
6. Weapon Skin Replacer - required to change some of the weapons to their own categories. In any case, this mod doesn't do anything in game, it's just a tool for modders, so this one should not bother you.
7. Ability To Slot Reassignment - same as 6, it is essentially a modding tool, so by itself this mod should't affect the game in any way. Also, consider using this mod that fixes some typos in Ability To Slot Reassignment.
8. Mechatronic Warfare Perk Pack - required. Abilities from it are used all over the classes. This mod can be replaced with the Mechatronic Warfare mod itself. There are slight changes in the abilities between the Perk pack and the full mod, but most of it works just fine. Do not use both the perk pack and the full mod together.
9. Ballistic Shields - required for the Pioneer spark. If you do not want to use the Pioneer spark, you can ignore this mod.
10. Immolator and Chemthrower abilities - see 9.
11. Iridar Spark Arsenal - obviously required. The entire point of these classes is to take advantage of the weapons introduced in Iridar's spark arsenal. If you do not want to use Iridar's Spark Arsenal, then why are you even using this mod? :)
12. Spark Arsenal Plugin: Shell Charges - optional. The mod will work correctly without, but using this mod is the preferred balance setting and the intended use.
13. Expanded Robotics Repair Facility - required. in addition to adding the repair slots, this mod also fixes lots of small weird things that are a bit wrong with Sparks in the base game, so it is required.
14. Custom Spark Classes Redux - obviously required, this mod allows Sparks to have more than one class. Note, that there are two older mods that claim to do this. Since these mods are old and no longer maintained, they have some issues which are fixed with the "Redux" version. Do not use the older mods, and they are marked as incompatible.

Happy Sparking!