The best time in year to go to Sweden and Finland is
from late May to early September, because this are
normally the warmest month. From October to April
there is winter, at least in the northern parts of
this countries, with ice and snow. If you go early in
the year you could have bad luck (like I had) and get
a little snow in the north, but you've got the
advantage that there are still no mosquitoes, not even
next to the lakes.
Road conditions: The E-roads are often built
as motorways and they are as boring as motorways. The
other roads are in good conditions and they are not
seldom better than in Germany. Only very small roads
are gravel-/mud-roads (depends on the weather) and
they are often dead-end-roads (up to 50km long).
Getting fuel: This is not a problem,
not if you've got a credit card (best Visa). At many
fuel-stations there is no desk were you have to pay,
but there are automats which will (hopefully) accept
your card or sometimes they also accept notes/bills.
The prices are about 1,15 Euro per liter in Sweden and
1,07 Euro in Finland (may 2002).