Hey OP, I had a similar bike building experience and aimed to make my used CAAD10 light as possible while being on a budget (student moment). Biggest and cheapest things you can do to save weight:
- Carbon saddle. Like $30 - $40 CAD and you'll probably save like 100 - 120g off of many brands. Unfortunately my carbon saddle didn't fit me too well so I'm looking for a regular saddle as I'd rather my ass not hurt over 120g.
- Titanium skewers. $20 CAD ~ and will shave off easily 50 - 60g off stock skewers. I use RISK.
- Carbon seatpost. I used Elita One.
- Kalloy Uno stem. Lightest stem in its class, costs like $20 and there's the Niu Ju mount to pair with it for an integrated bike mount look. Handlebars, I don't quite know but people here like the RXL SL. I had Toseeks but I personally didn't trust it quite enough (was about $40 CAD) so I just bought an alloy bar. But for carbon, you can definitely shave off almost 100g ~ with carbon ones.
- Lightweight bottle cages. Each cage I have weighs 11g and I shaved off 64g ~ ish off stock plastic ones.
- Carbon top cap + lightweight compression plug. I wouldn't bother with this if you don't know what you're doing here, but it's an easy way to save like 40g.
- Cranksets, you can get a carbon one from RIRO. Easiest way to drop a ton of weight but is $$$.
- EXS Air Tape is a good option for a pure lightweight build and drops a surprisingly amount of grams (roughly 50g?). But I definitely didn't quite enjoy the feel as much, so I bought name brand bar tape. You know those smooth, foam yoga pads? That's what the EXS bar tape texture felt like, but in incredibly thin tape strip form - zero padding.
- If you're ballsy enough, you can get a pair of EE fakes but they don't brake as well as the real thing. I'd rather be able to brake decently well - if you climb mountains, you've still gotta go down the mountain somehow. I bought an entire 105 R7000 groupset for the build and I'm very happy with the results.
- I believe that there are lightweight pedals out there, I forgot but Tracevelo definitely has a video on that.
- I don't know about cable liner and hoses. But my CAAD10 is from 2011 and runs external cabling, never had an issue in cold and rainy weather (Lower BC). Also, no idea about cable guiding. 3D printing's probably your best bet.
- Carbon clinchers are pretty cheap and a reputable pair is just as bulletproof as mainstream brands. Elitewheels or Easedon sells nice rim brake wheels on the cheap while being lightweight, but if you're still not sold on it, Ksyriums are probably your best bet (used).
And finally, get a pair of nice GP5000s. They are like 235g and will shave off weight off of heavy stock tires, while having much lower rolling resistance.
Also, the Sora groupset is perfectly fine but definitely quite heavy for a lightweight focused build. I recommend getting an used Ultegra 6800 groupset as it's the generation where mechanical shifting has been perfected - being 11 speed, parts readily available for replacement and doesn't cost as much. But 105 R7000 definitely works fine (although it's like a 250g weight penalty).
Hope this helps.
