Bought separately, new, those parts would cost about £1600. Remember the crankset / bottom bracket is press-fit BB30 which is trickier to install yourself, so maybe best buying the complete bike, if somewhere has it in your size for a good price. How tall are you? I guess 54cm is for people about 5ft9 / 5ft10. Don't know much about 105 5800 vs Ultegra 6800 - both are meant to be very good - but I'm gonna go for Ultegra. Ultegra should be more robust than 105. It's Dura Ace 9000 that has some parts which people have had issues with (cassette, levers fraying cables - although that has been fixed in the recent models).
Bought separately, new, those parts would cost about £1600. Remember the crankset / bottom bracket is press-fit BB30 which is trickier to install yourself, so maybe best buying the complete bike, if somewhere has it in your size for a good price. How tall are you? I guess 54cm is for people about 5ft9 / 5ft10. Don't know much about 105 5800 vs Ultegra 6800 - both are meant to be very good - but I'm gonna go for Ultegra. Ultegra should be more robust than 105. It's Dura Ace 9000 that has some parts which people have had issues with (cassette, levers fraying cables - although that has been fixed in the recent models).