I´m from Denmark(you know, the small country, with polar bears in the streets
My parents live in Holland, and i´ve traveled allot across Europe.
First of all, u need to think about some sort of Visa(visum), or at least a working permission, otherwise your in big trouble if you take a job, somewhere over here.
Almost every western European country learn there young ones English in school, so they speak it almost everywhere, however some populations are more willing to do so, than others, fore example the French are not likely to speak anything else than french, and the Germans have first got it in there schools in like the 80´s, so it´s only the young population that speaks it.
the Dutch however, are very good in the english language, and so are any of the Scandinavian country's to.
Great britain and Ireland are of cause english speaking, but be aware that it rains A LOT in England!!
But on the other hand, they have the little island called "Isle of man", witch have NO speeding limits
(The same as some parts of the german "Autobahn" )
About the driving license, I´m not quite sure, but I´m 99% sure that you legally can drive here with the license that you already have, but the rules can vary from country to country.
About longest driving season, the rule is, that the longer to the south you go, the longer the season. Here in Denmark where I live, the season is possible from March to November, but only funny/nice from like April/May to October. The longer to the south you go, the warmer the weather.
Country´s like Spain, Italy or France are possible to drive almost all year round, only few days witch are to cold/bad weather for my preferences. But these country's speak very poor english, almost nobody, except in the big city´s speak english, so have that in mind.
Speaking about job possibility's, what are your skills? I´ts for example very easy to get a job as an "computer guy" even if you only speak english, as many major computer companies have english as there number one language internally in the company. Also construction companies employ "non native" workers... Limit is the sky
Have a nice trip