Groupset for bike with internal cabling

I decided to go ahead and order a new 105 complete group set (the latest model with direct mount brakes option).
Cheers for all the advice and good reasoning. It definitely would have been wiser idea buying decent used components (in good condition) than throwing the same money at new low budget stuff (Tourney) that would probably not have even lasted as long and performed far worse. A bullet dodged there for sure.
It was near enough to 500 euros for the 105 set so it was an expensive hit but the frame is mint new and to be fair a decent new frame like this deserves a nice new groupset.

Now shortly will see if I can fit the groupset with the internal cabling requirements of the frame. I highly doubt it. Will very likely end up in a local bike shop paying for it. If so I will at least request to watch while it's done!
As for wheels I'm going to have to wait for my finances to recharge before buying them. Therefore initially I'll transfer the cheap wheels of my Triban 500 onto the new frame.

Finally, StraelGuy, while I no longer need a derailer the offer of that high quality 105 rear derailer for free was incredibly generous and kind. Very, very much appreciated. Some damn nice bikers around here!

Thanks. Good to know. I've never read anything but praise for Shimano 105. Sounds like they are the entry level of professional.
I couldn't afford- or justify saving- above 105 anyway since I paid 200 euros for the brand new frame (A Btwin Ultra AF 920, with handlebars and seatpost incl) and if I buy some decent weight wheels (light-ish pedals I already have) and the new 105 set I am going to be up to about 750 total.
Originally the bike had Ultegra groupset and Mavic Cosmic wheels (the complete bike retailing about 1,199 euros i believe).
It certainly doesn't take long for a newcomer to see when given the price of components, people often just buy bikes with those wanted components just to strip and then flip the frames to try to save 100 bills.

Still I think the frame was a fairly good buy. I know it's nothing special in terms of weight even as an alloy frame but I could put even something like a Sora set on it and it would be a considerable upgrade over my current Btwin Triban 500.
I couldn't really afford a new bike for the new year so I decided this was a good project to try and get a slightly better bike, even if, at worst, I end up only putting the components from my Triban 500 onto it (less the brake calipers which I will need to buy new as the Ultra frame takes direct mount brake calipers).

I'm still torn between what to do. Putting budget well used (although still working perfectly) components from my Triban 500 seems lame, underkill, especially as wiring internal frames is said to be quite an awkward process.
Another part of me wants to just buy a cheapo Tourney groupset (available brand new for about 150 euros with only the calipers not included) and be done and dusted for about 300 or so total on top of the frame cost.

But even that option seems lame. In reality I need to get more significant weight drop than that (vs my Triban 500) for this to have been a clever good value for money plan.

Thanks again for all the feedback. I will take a decision shortly. I could always probably re-flip the frame for the same as what I paid but I'm still convinced that this can be a sizable and good value for money bike upgrade for me if I do it right. Also I would like to gather the experience of trying to build a bike by myself from scratch with components.

Thanks for the info and very helpful link to site that sells with customizable options. Likewise to Canyon48 and Kil0ran.

Part of me is now tempted to just buy the 105 direct mount calipers and then try fit the components from my current cheap road bike (budget components but only a year or so old and perfectly working) on the new frame. Probably better to experiment that way first rather than with a nice new 105 set, then decide thereafter if I want to upgrade.

And yes, it wouldn’t surprise me if the internal cabling routing task left me red faced in a local bike shop cradling my components. I think the outers are still in place and perfect...seems to be a genuine never riden new frame that as the seller claimed was bought to be stripped of it's components which included Ultegra and somewhat expensive wheels.

Will try update this thread to how i got on. Thanks again, much appreciated.