Any tips for efficient mod making?

[Perturabo]

Something about stuff that allows to save time and effort?

[Lieste]

Start small (ish) a few ammunition types, weapons, one basic infantry formation (to Regt level?) with the supporting weapons and HQs and Supply elements.
It is possible to add placeholders for all intended ammunition types/weapons/vehicles, and this makes the XML a bit more ordered, than inserting elements "as needed", but this goal is possibly unattainable in an evolving dataset, and unnecessary.

Eg:
Rgt HQ
Rgt Ech
Bn HQ
Bn Ech (optional)
Rgt Inf Guns
Rgt MG Coy
Bn MG Plt
Coy - Infantry

You could alternatively start with a mechanised force, but I know your interest is rather more WWI/Steampunk.

The sides/forces require national 'flags' as images, and 'none' isn't supported - all unit graphics can be left to add later.

When building your forces, you will want to plan ahead, on paper or in a spreadsheet. I prefer to track 'everything' using a sparse table, but you can also work with lists if you prefer that. You will also want to review the content of the dataset and your plans after completion - it is easy to miss a step/jump over a force or mess up accuracy/penetration data etc.

A more 'efficient' method would be to start with an existing Estab, and change data to suit your mod, rather than to build an entirely new file - you can either work by adding new data alongside the old, or by removing/replacing it. The latter is 'cleaner' not containing excess elements to your needs, but the former is apparently preferred.

Save, compile and test* frequently - this helps pin down errors to smaller sections of the DB - (ie those recently changed). *Minimum loading into SM, but ideally a small test scenario in game, as this will help highlight imbalances in weapons performances etc, though the effect of equipment is relatively modest.