That's quite a loaded question.
Boosting your presence in the industry is more about sharing your process in my opinion, so as you learn - share this with the community on your social networks. Also credit the sources of information as this gives you credibility and strengthens your contacts in the industry. Advice I wish I knew earlier.
Trends come and go - design is a solid foundation to build upon. Read design books, interior design magazines, check out what's trending on Pinterest or popular design social feeds, go to libraries and pick up random books for inspiration on topics outside of your expertise which can give you new ideas etc.
Some of those market places you mention have different users and requirements, its in your best interest to research each market with that in mind to see if your content fits their strategy. This also applies to the artists looking for content, those who work in architecture compared to those working in children's film/tv are looking for different content or are on different platforms. This also goes for technical specifics such as geometry type (subd, quad...), material/texture setups, render engines, 3d print etc. My advice would be find your target market and watch for scope creep - even for veterans its easy to get off track and start implementing unrequired technical changes because its the new 3D trend - examples would be PBR, trim sheets, quad-topology etc. Sure these are great things but remember your target market, maybe your particular audience has no need for (some of) these things specifically and cost you large amounts of your time - quality and consistency are the most important factors, you can always update the standards later once you have established a good routine of shipping your content and field testing.
There is nothing stopping you from starting small with props/assets with a larger goal in mind such as kit bash or asset packs, in fact Cgtrader make this easy with collections so as your content grows you can package fitting items together. This can also be a good motivating factor to complete larger sets of work with little wins along the way.
In regards to what I make or buy, I think the thought process should be adjusted a little. The goal for content creators should be to make things that provide value to the customer. Important factors are; is it in demand, is it widely available to purchase already, can you make it better, is it difficult to make, does it save the customer valuable time etc. As long as your content provides your customers with value and keeps them focused on tasks that don't interest them then you are on the right track.
If you want to aid research I advice you reach out to artists individually, those who's work you enjoy most and chat with them. In regards to your business good luck, I think planning is crucial to any large undertaking and investment of your time.
