If you must paint this stained wood, a light sanding with 4-O steel wool or 320-grit sandpaper should be fine. All you're doing is roughing up the surface coat, usually poly, which will let the paint "key" to the surface better.
Be aware of the finish originally used on the wood; only poly will take a latex topcoat well, while on most other finishes like varnish or oil-based finishes, latex will not bond to the surface properly; it may peel easily, or even bead up when applied. If this is the case, roughing up the topcoat is not enough; you will have to sand off the topcoat to get to raw wood, and on a profiled wood piece like mouldings, this can be difficult or impossible.
Also be aware of the type of wood; certain woods are "open-grain", and will absorb paint deeply into the structure of the wood, requiring many coats to "fill" the wood and get a solid color on top. Otherwise, the grain and any knots will show through the final coat until you put 3 or 4 thick coats on. If you have to go down to bare wood on an open-grained wood, you have to seal the wood with a product that is compatible with your paint base.
Surface prep is one of the most important factors of painting, it takes most of the time. If the surfaces are clean of environmental contaminates, fireplace and cigarette smoke for example or hand prints around door knobs, then you could forego wiping down the trim or places were heavy deposits of "stuff" build up.
There are "liquid sanding" compounds that dull a surface to eliminate sanding, But I can't vouch for those. Hand sanding at best for detail areas, use a pole sander for larger wall surfaces, use 120-180 grit if you plan on priming the wall again. This will be needed if you plan on changing the color to something that may not cover on one coat. Use 220 to de-gloss the surface, if the finish paint can be done in one coat. Otherwise you can see the scratch marks through the finish coat (with heavier grit), if you use gloss paint. This effort over the old paint will also remove other debris that inevitably gets in the wet paint as it is applied or while it dries, such as lint, hair and fuzz, paint runs, you name it.
Use the what may be now the not-so-reflectiveness of the once was glossy paint to determine how well the scratch pattern is on the wall.
With a pole sander, it may only take an overlapping pass in each direction (left to right, top to bottom) to accomplish this. This will help keep track of what you done already. Better than waving around all over and hoping you caught all the area.
No sanding job will be 100%, the idea is that the new paint will have enough to bite into to hold up over time.
The visual amount to look for? Picture what a comb or brush for your hair would look like if it left marks on the wall after one or two passes. Of course, what you will be doing in reality will not be uniform as my word picture suggests, but the idea is to have more scratched wall surface than glossy, with no large spots that are still glossy like it was never sanded.
Best Answer
Because "it barely had any glossy look to it" and you sanded it and cleaned it well means that it has been properly prepared! Good work.
Feel free to prime and paint it now, but do yourself a couple favors and buy good quality paint and professional grade brushes. I cannot stress how much a difference using quality applicators will make. Just build time into your schedule for thoroughly cleaning them and they will serve you well for years.