I have two sets of wheels, one a 32 spoke with 14mm internal width and one that is 20 spoke 18mm. Has anyone used a 20 spoke wheel for regular commute? Does it stand up to 400 miles of commute a month? The 14mm wheel I'm guessing won't take more than a 28mm tire.

Any thoughts or experiences?

Well going to say no on that only because you gave us little information about yourself or your commute or anything like that. If commuting probably the more spokes is better but in the end a well built well is most important granted with more spokes tends to be less catastrophic if it fails.

Yes wider tires are important and do help a lot but I think you can probably do a 28-32mm tire in those rims and maybe a touch wider but yeah it is a bit narrower.

I would let folks know what wheels you have or if nothing commercially available list what parts are used and then also tell us what your roads or like or where you are commuting and also how much you weigh and how much you are carrying. We are not all knowing (though I know the most and have a bigly brain...LOL) so you have to give us the info so we can help you but in general more spokes probably a better commuting wheel (up to a point) but a hand built wheel from a professional vs. a crappy machine built wheel will likely last longer and can be better tuned to a rider.

Tire max on wider rimmed wheel?
Schwalbe has some tough tire options at 30mm. And probably many others.

I did a 60 km round trip commute for 25 years on tires ranging from 700 x 23 to 700 x 32 in width. I never worried about rim width. My last setup was 700 x 32 tires mounted on rims with a 14 mm inner width. Worked just fine for a couple of years and about 18000 km

I weigh 150 pounds ( I carry a backpack that weighs 12 to 14 pounds). My commute is mostly on tarmac. I ride mostly paved trails. Average of 500 miles a month. The 20 spoke wheels are Shimano wheels (hub and rim) bladed spokes. Hope that helps.

Getting better, probably would stick with the 32s most likely but not sure on those. I wouldn't go bladed spokes or straight pull which I am guessing those Shimano wheels might be because should you need a spoke it is probably not something most shops will have. I don't know if proprietary but possibly (again not sure of exact wheel and can't check specs or remember most of their system wheels anyway). For commuting reliability and serviceability are key factors. Yes you are pretty light at least compared to me you are a feather but still wouldn't want to be struck down using a lightweight wheel especially if not racing. Some tarmac and paved trails can be quite nasty sometimes and your level of commuting is significant so yeah I would say go with 32 or at least 28h wheels. I would also ditch the backpack get some air moving on that back and be more comfortable in all aspects.

20 spoke, bladed, 18mm, Shimano branding? I'm guessing it's got about a ~25mm rim height, as well? Sounds like a WH-R500, or an equivalent thereof.
Those Shimano 'Road Sport' wheelsets have a reputation for being pretty solid, if somewhat heavier than similar offerings from Fulcrum or MAVIC.
I've put 500 miles in a single week on a set of those (running 28mm tires) and I weigh significantly more than OP.

I'm also guessing that those super narrow 32h are the old 'box section' style rims as well. In most cases, the modern 'semi-aero' profile rims are stiffer than the box-section rims, allowing them to be as 'strong' if not stronger, with fewer spokes.

Skinnier tires work fine, if they are inflated properly, but skinny tires seem to need topping up for every ride.
If you are riding bladed spokes on your commute, you may be using the ride for conditioning far more than I would associate with commuting.
If I were commuting, I would go with less maintenance so I didn't have to pump up the tires what I was running late, and a flat was less likely even with less than rock hard tires.

I have run used 32mm cyclocross tires on old 14mm rims for years on my town/grocery bike w/o issue, at 190#. I am careful with inflation and would not bomb down a decline with a sharp turn at the base.

At 150 lbs you aren't going to have much problem on whatever wheel you choose.

If you do your commuting at the speeds and conditions similar to what they have to ride for the Paris-Roubaix, then you might need to better consider your wheels. But otherwise it's no big deal.

Put on a tire that will fit the frame that provides the best cross of weight, comfort, and flat protection.

30 years ago mtbers were bombing down trails with almost 2” wide tires on 14mm road rims rolled to 26”.

And I would think today’s tubeless ready tires make it even less likely to unhook from a narrow rim.

John

I'm more a party pace person. I'm guessing that simplifies this whole thing. Thanks