groupset advice please

Depends on what terrain, type of riding, your fitness...and bike of course... Generally new bikes are being sold spec'd as 50/34 & 11/32 as the "standard" now to cover all markets and riders, where one time it was 52/36 & 12/25... I'd go for a gear calculator for gear inches ( some online ones will give speeds achievable in on click) as a guide 113 inches will give 30 mph and low down gearing most mountain bikes are 18 gear inches....with that in mind bikepacking guys on gravel bike will be looking for 25 ish gear inches....on a double front 46/34 & 11/36 you'll go anywhere...lol... A lot to consider but use a gear calculator to work out best combination for you...it's getting the hills right for you and the flat speed....there is no right or wrong..... I've a customer who is on 52/36 and 11/28...he's now dropping to 50/34 after 10 yrs on that gearing but keeping 11/28 and the new kit is going on next Tuesday.....good luck... whatever you choose...if you go large up the back....make sure you've a derailleur with the capacity to handle the cassette

There are some variables here: two chain ring ratios (52-36 / 50-34), and numerous cassette ratios (34-12 down to 27-11) and then there are a few unknowns: how long have you been cycling; how heavy are you; and just how hilly is it: Kent/Sussex hilly; or North Yorks fells - because one will slow you down with the wrong ratio and the other will have you walking (and I'm doing an injustice to some avoidable nasties in Kent & Sussex. In North Yorks you can't avoid them)? 

I'd be tempted to go 52-36 and 34-12 on the basis that a 34 chain ring is really no use at all on anything but very steep climbs. You could mix it too. I have a 50-39 on my Factor 02 for this very reason (Kent/Sussex avoidable nasties), but no need for the leverage of a 53 outer ring.

You can get a used 50-34 from eBay relatively cheaply and switch it over with an allen key in a few minutes.  Last time I looked,  52-36 held their values better on eBay, so rather be a seller than a buyer.  As you get stronger, you can then reduce the ratios on your cassette too or just keep spinning.  You can solve your long / short cage derailleur issues with an adaptor from Wolf Tooth.

Now, you have to tell us where you intend to ride....Locked down in London, I'm curious for one. 

Not easy to answer. What I will say is that I didn't get on with the 50-34 setup. It is a few years ago now but I remember that I was having to change too often between chainrings on my lumpy home terrain. On my last new road bike in 2016 I settled for 52-36 with an 11-27 cassette and that works fine for me.

Classic 'it depends' question/answer.

For chainset you have 2 options: 50/34 or 52/36 (I'm ignoring the 53/39 option).

For cassettes, 11-28, 11-30, 11-32 and 11-34. You will need the 'long cage' rear mech for the 11-34 and the medium cage for the 11-32.

Work out your speed in your top gear at 95rpm. At 52/11, that's about 57kph; at 50/11, that's about 54 kph. I'm going to put it out there and say 50/11 will be enough if you're not at the sharp end of races.

That selects you a 50/34 chainset.

So, cassettes. Work out your bottom gear. 34/34 is 10 kph at 80rpm. 34/32 is 11, and 34/30 is about 12.

The selection here is up to you. How strong a climber are you? How hilly are your rides? Will you ever take the bike to real mountains?

If in doubt, err on the easier side - you can always pedal faster or select a harder gear, but once you're out of gears and grinding... The only real downside of a bigger cassette is bigger jumps between the gears. That is most an issue for racers.

Personally, I'd say 52/36 cranksets and 11-28 cassettes are for racers and strong riders. 50/34 + 11-30 suits sporty riders and club riders in flatter areas, while 50/34  + 11-32 is a good option for most club riders. Pick 50/34 + 11-34 i you know you need the extra help or plan on taking trips to the Alps.

How long's a piece of string?
Unfortunately gearing can be very variable depending on who you ask and fitness levels. There can then be a few different ways of achieving the gearing depending on preference, for example: my summer bike is 11 spd and 50/34 at the front, 11-27 at the back which helps me tackle long/lumpy rides...my steel frame bike is 53/39 and 13/29, which is fairly similar. Some folks I know need an easier gear at the back and ride 50/34 with 11/30, or even more.
Old school for references is actually best in that you convert to inches (just the distance a wheel travels per crank turn) and then see what your options are. Fortunately there are some great online tools to help...and changing a cassette is easy with the right tools but big cassettes may need a long cage derailleur!
Have you a reference setup that you have tried? Failing that, most folks will go Compact (50/34) with 11/30. Give something like that a go. If it doesn't work then you can use an online tool to see what works for your preference (bigger or smaller gears). EBay always works well for effectively swapping without a big hit on cost.