First time Road-biking. What clothing?

This is the best all round
This is the best all round bit of kit I’ve had in 35yrs cycling all weathers:

http://bikemagic.com/gear/reviews/bontrager-rl-thermal-soft-shell-jacket-review.html

It is practically waterproof but feels like a jersey and is good for temperatures from below zero to about 16degrees C without getting too hot.
Other advice would be shorts and leg warmers -Don’t go overboard on the shorts and buy Assos or something – I like Lusso or Endura. They all tear should you have a tumble but you won’t need a lottery win to replace them!!

Then a good base layer under a jersey of your choice. Again my preference for fit, comfort and price is a DHB item from Wiggle in either short or long sleeve.

Good luck and just pedal!!

In those temperatures I’d
In those temperatures I’d select from the following according to the day:

3/4 length bib-shorts
short sleeve base layer
short sleeve jersey
arm warmers
thin windproof shell or gilet small enough for jersey pocket

The advice about several thinner layers giving you more options is good.

Don’t know far you are from a bike shop but a lot of them will be holding sales at this time of year, as will the big mailorder houses but the reason I would advise on an actual bike shop at this stage is you can try on several options and seek the advice of other local cyclists who are experienced in the climate. Shops tend to stock clothing they like wearing.

Final piece of advice; if you ride away from your house feeling warm enough you’re probably going to feel overdressed within a few kilometres.

Yes I reckon a softshell
Yes I reckon a softshell would be too warm – on all but the coldest days I find mine too warm here in the UK with all but a short sleeved base layer. We’ve had a mild winter so far here in the UK, but most days I’ve ridden in a merino base + either bib longs or bibshorts and leg warmers, short sleeved jersey and either road.cc armwarmers or some Craft ones. In the wet I’ve maybe usually foregone one top layer and added a breathable rainshell.

Given where you are and your likely riding temperatures I’d suggest short-sleeved base/jersey combo matched up with some armwarmers and a gilet with a windproof front would be the way to go on top – especially if you don’t have to worry about rain.

Those Endura tights are good too, but I’m wondering whether they might be too warm for you in Greece (maybe not, to some degree it’s all relative) but Endura are based in Scotland where it’s properly cold so their kit is warm – certainly you won’t need to worry about getting cold in them.