The 3000 mile interval was written by people who sell oil and filters.
Oil is cheaper.
Reality, if your oil is noticeably dirty (black), if you drive in dusty, extremely hot or cold conditions, or work an engine hard, the service interval likely should be shorter than the manufacturer's reccomendation.
I change oil every 3,000 miles and have driven a vehicle with an engine I rebuilt (1975 Chevy van 350 V8, 4 bbl carb) 119,000 miles on that rebuilt engine (vehicle total 296,000 miles).
The idea is to keep circulating carbon and dust from circulating in your engine, because that causes wear. Also, combustion byproducts are corrosive and can build up in your engine oil, so the 6 month interval at a minimum is probably a good idea.
Warmups: some yes, some no.
The Ford/Lincoln 400 CI V8 was notorious for becoming carbon fouled if it sat and idled to warm up, the 460 (Ford/Lincoln) performed better after a brief warmup (3-5 minutes).
At this latitude, if it is below freezing, I prefer plugging in the engine heater and having the engine warm when I start it. Some folks use lower temperatures for a guide, say, 10 above or even zero, but my older vehicles seem to perform better if I have them plugged in when the mercury dips into the twenties.
Synthetic oil helps, too, as it makes cold starts easier in low temperatures and helps get oil circulating in the engine better when it gets cold out (below freezing, and especially below zero).
Best I ever had was sold by Interstate (9 years, subzero winters), next best by NAPA (7 years). If you have to get a jump start, let the vehicle charge the battery for a bit. When you get home, check battery connections for corrosion and clean them as needed (or have a mechanic do it, but the tools only cost a few bucks and last a long time), put a battery charger on the battery at a low setting (2 amps) and let the battery charge. The newer chargers can auto regulate the charge rate. Make sure electrolyte levels are where they should be (check them before you hook up the charger with the engine off), and keep in mind that really hot weather is just as hard on batteries as really cold weather.
Anyone who drives should be able to do a few basic maintenance tasks.
I’m fortunate I guess to have a garage that never dips below forty, even during the coldest winter days. Those nice warm engine blocks do well to heat the place back up too.
Longest battery life I ever had was on a 96 ford F250. The original battery was replaced in 2007. maybe 2006.
Seems to me the main thing you need to do to make a vehicle last a long time is to drive it regularly, park it indoors, don’t get in an accident(when you do, the vehicle seems to start having problems later on after the repairs are made), and once it gets about 80,000-100,000 miles on it, you need to start checking oil levels frequently and keep it topped off.
For a few years around 1990 my job involved running around jump starting cars. Below about 10-15 degrees, that's all I did, and often the business phone would be off the hook by the time I got in at 6am (already had enough business for the day).
Vehicles with Interstate batteries were far more likely to start. [Now, before anyone asks why if they're so great did you need to jumpstart them, there are other reasons why vehicles don't start in the cold, and often people run the battery down while trying]. Also, that is the brand that we sold in the shop. Replacing an Interstate before, or even a couple years after, the warranty expired was rare (compared with other brands, where batteries going out before the warranty was pretty common if not expected).
Motorcraft (Ford) batteries, OTOH, might last a couple years, but were worthless in the cold. IMO, their only value was to hold the battery tray in place.
That was nearly 20 years ago (sucks that I can say things like that these days), I don't deal with batteries these days, or live where it gets cold, but at that time Interstate was head and shoulders the best.
Changing your oil before the recommended time to me, is a pretty inexpensive peace-of-mind issue. [Even though mine takes 8 quarts.]
I think warming a car up is imperative, especially if it is a HP car, even after it’s warm, I try not to full throttle the engine for a while.