^^^ this^^^

You and others have already mentioned the stem I had a UO-8 with an Ava stem, and it snapped completely through on me. Thankfully I was in the driveway and not heading downhill. You really, really need to swap out that stem. One additional point to consider - it is very likely the clamp on a replacement stem is not compatible with your existing handlebars, and you would need to replace the bars and stem at the same time.

Trading out the wheels for a set with alloy rims will make a very noticeable improvement in riding pleasure, especially the improvement in braking. You could go with wheels from that era, or a totally new set - both options have positives and negatives.

If you want to scrounge up a set, many mid-70's Schwinns come with Normandy made "Schwinn Approved" high flange hubs laced to 27" alloy rims. Many Japanese bikes had wheels that were very derivative of these, with high flange Sanshin or Sunshine hubs laced to Araya or Ukai alloy 27" rims. There's millions of these sets around. Pluses - cheaper and will look 'correct' on the bike. Minuses - you might need to search for a while to find wheels where the hub, axle, spokes, and rim aren't basket cases.

If you want a new set, the Sun CR-18 rim is a great value and looks correct on 70's bikes. However, most wheelsets available built with this rim use modern low-flange hubs. Velomine has a set for $110. If you want something new that looks period-correct, Velo Orange has an absolutely gorgeous wheelset with high-flange hubs laced to really nice rims. They're more expensive at $380 for the set. Pluses - very little work to get up and running compared to hunting down old parts. Most likely they'll give you more miles before service is needed/spokes break/sidewalls wear through Also, new rims have a sidewall profile that does a better job of holding on the the tire bead than some older rims. Minuses - $$$, possibly looks out of place if low flange hubs are used.

Another option is to unlace your hubs from the steel rims and lace them up to alloy rims.

'You can keep using the headset and bottom bracket as long as they aren't damaged.

You mentioned you are getting new cables, you probably should also replace the brake pads and tires/tubes.

Looks great so far ad I love the purple color - never seen that shade before on a UO-8.