Good to hear that you might be able to convince your company to hire a consultant upfront as opposed to after the fact. This is a much better proposition that will ensure you don’t waste your time coming up with something that isn’t useful and allow a consultant to do much better work than merely reviewing what you develop.
From my perspective, I see this as much more of a branding issue than a design one, base on what you have said about your company and products. Before any “design language” is developed I think it would most important to first have a clear position analysis and development of the brand. That is;
-how is the brand currently perceived?
-how would you like the brand to be perceived?
-what should the brand stand for?
-who is the brand targeted towards?
-how is this achieved?
-how is the brand differentiated amongst competitors?
This then becomes the foundation for any design language be it in graphics, product, marketing, etc.
IMHO, hiring a traditional ID company focused on product will not get you the right results. I have seen this many times. A company thinks they need a design language (often referencing Apple or other such design leader), an ID company comes in, sets out a guideline of making everything X color, X shape, X style, etc. and leaves. The product is executed following this direction, but there is no link to the greater brand, position in the market, etc. and the design language dies when results are not achieved.
If you can bring in a branding consultant rather than a design consultant (or ideally a firm who does both), I think you will achieve a much more thorough and in-depth result.
At the root of it, any design language should be firmly connected to the brand, and it sounds as though this is not the case. The simple fact that they asked you to create the design language yourself and not initially hire a consultant (and that you are designing product from an engineering experience rather than an ID one), makes me think the company doesn’t really see the value in design and branding. This is very common (though unfortunate) in engineering-focused companies, but it sounds like perhaps you have a good opportunity to change it.
On the $$ side, see if you can layout the potential from a bottom line view to your boss. Hiring a consultant may cost $20-$30K (or more or less depending who they are and what they do), but this is likely a very small drop in the bucket to the company revenue. If a design/branding exercise can increase sales even 3%, you’ve paid for the consultant in 1 yr if you are a 1M company (which is pretty small).
At the very least, an initial analysis of where you are now, not even touching on where you want to be can be very educational for the company and point you in the right direction.
just my perspective on the issue. best of luck.