Wheels with 48 spokes should take a lot of abuse-
I always try to play my spokes pretty tight- a wheel tends to round itself a little bit as you get tighter-
If the rim is new I generally mostly tighten when I'm truing and rounding a wheel- when they are tight, the loosening of spokes to round or true is minimal-
with 48 spokes they may not need to be really tight- but they shouldn't have much flex either
I had a Park jig and built up all my own wheels when I was racing back in the '70s- mostly 36, three cross tubular sew-up rims then
and I'd build up more wheels these days, but the friggin spokes have gotten too expensive- I recall paying 10 and 15 cents a spoke- now they want a dollar a spoke- or more!- so it's just as cheap- even cheaper- to buy wheels already built up- even with the high cost of shipping-
I've wondered a bit why that is. You'd more than likely be paying about $48 to buy the entire set of spokes for your bike, with 48 spokes, and I guess the manufacturers are not paying as much for the spokes.
anyway, when you're building it up and truing, you need to gently tension the spokes by pushing lightly sideways on the rim- all the way around, three or four times on each side-
that's when you hear that sound described in the post above- that's the sound the spokes make setting themselves in the nipples and the rim- otherwise they can hold tension that pops out later-, changing the adfjustment-
and you usually have to retrue a time or two after riding it- I usually tighten, until they feel tight and the nipples get harder to turn- and only 1/4 turn at a time near the finishing- and when they are tight then you may have to slightly back some off to get the side to side true-
but the rim tends to round itself under tension- that is if you've started all the spokes even- I generally guage that with the spoke thread showing relative to the nipple- get each nipple end at the end of the spoke thread, or the same length at least-
and then methodically tighten each the same until they start getting tighter and don't flex much- then it's time to start visually checking the rim on the jig or the bike, and tighten them discriminately as regards to true and round-in smaller increments as you get closer to finishing.
i've built up a few lately the past couple years in this fashion and just using the fork and brakes for the final true- but it is nice to have a wheel jig. A Park stand was $50 back when- more now I guess.