I'd personally not buy any road frame without disc brakes and clearance for 32mm tyres. It's getting much harder to get good rim brake wheelsets now and higher volume tyres are just nicer to ride. The choice of groupset would influence whether fully internal routing was appropriate as I wouldn't want to run mechanical brakes with full internal routing. Getting a T47 threaded bottom bracket also makes life easier.
I've personally had a frame from Light Carbon and am happy with the quality, and currently have a frame on order from Mondince.
i strongly agree with this advice.
I've just up/side-graded from rim brake to disc. Rim brakes are great, but for most of us the advantages of disc brake bikes with wider clearance really mount up. Obviously, if your primary goal is to win the UK National Hill Climb Championships then it's rim brakes all the way, baby!
I went for an ICAN FL1 frame for my first build, which I'll happily recommend. Why?
- It's well made, with smooth internal surfaces and carefully machined interfaces - bottom bracket, headset and brake mounting points - meaning that it's easy to build with and, so far as I can tell, it rides well.
- It's largely non-proprietary - T47 BB, FSA ACR compatible headset and round seat-tube. This gives you lots of choice for compatible 3rd party components, such as cranks, handlebars and seat-posts. (It only misses out on the UDH standard for rear derailleur hangers - so buy a spare or two).
- It's cheap! Not Airwolf / Twitter cheap, but cheap.
- It's relatively light.
Aesthetics really do matter though and you might not like the old-fashioned non-dropped seat stays. Equally, if your heart is set on SRAM then UDH is pretty much a must. As others have mentioned, geometry needs to be in the right ballpark, so try comparing your Cannondale against some of your candidate frames using a site such as geometrygeeks.
You mentioned buying parts incrementally, which makes perfect sense. However it would be smart to pin down decisions on frame and therefore both bottom bracket standard and internal vs semi-external cable routing, cranks and groupset before you buy anything. This way you avoid some painful incompatibilities down the line.
For a budget limited build, the decision, in roughly increasing levels of cost, between these hydraulic disc groupsets:
- L-Twoo or Sensah mechanical
- Shimano 105 mechanical 12 speed
- Ltwoo or Wheeltop electronic
- SRAM/Shimano electronic
is a really interesting one. Any of these options can be made to work, and your choice may come down to the level of discount available. I stretched my budget by going for Shimano electronic which made cable routing and gear-shift tuning much easier and probably bought me reliability, but purchased from AliExpress which might make any future warranty claim a challenge.
For BB's: all can work fine, but I would choose a frame with either a threaded BSA and hence 24mm steel (or Ti) spindle cranks or a T47 and 29mm aluminium or 24mm steel spindle cranks. These are likely to be the most straightforward options.
Choosing compatible parts and trading off cost/weight/reliability on different components is a big part of the fun. It's not essential, but it may help you (it will!) to document your decisions as you go in a build-list spreadsheet.