As with any outdoor activity where you’re ‘active’ you have to accept that you’re not going to stay completely dry, so the priority is warmth. Temperature management.
Windstopper bib shorts/tights are a must imho. I have some Gore Next2Skin bib shorts I wear with windstopper leg warmers when it’s wet/cold. I wear Sealskinz socks with neoprene or rainproof overshoes. I put the tops of the booties under the tights, but even then your feet are going to get soaked, unless you wear a drysuit! So all about warmth.
I love Castelli WS stuff, and if it’s wet/mild, I just wear a Perfetto Light/Gabba with base layer and warmers. If dry and cold, I wear an Alpha Light jkt as I run hot.
As far as rain shells, I’m yet to find the perfect one. I have an expensive Endura Pro SL, but it has no ventilation, a short back and I sweat like hell in it. So I bought a Sportful UK Rain Jacket on eBay for £20 and it’s way better!
Money no object? I’d like to try the Assos Sturmprinz jacket with some Equipe RS Winter bib tights. But that’s a near £700 combo.