How long have you got before your ride, 8 weeks?. It may take you a few weeks to get used to them and get the positioning right. It took me 10 days to get it right moving from toe-clips. You also have a period of 'adjustment' as you get used to using them and it becomes 2nd nature to clip in and out. All that said you will get huge benefits from them and for the journey you plan I'd say they'll make a big difference. Whichever system you get, setup is crucial, get it wrong and you'll have knee and IT band problems, so once decided on a system, that'll be your next post
So system wise, whichever you go for, you'll need to buy pedals and shoes. My only experience is with the Shimano spd system, which works well for many and is used by mtn bikers and roadies alike. It's advantage is walkability. It's possible to walk in the clips quite normally whereas other systems are OK for cafe stops but that's all but have other advantages on the bike.
For my own system I have Specialized Tahoe shoes,
A520 pedals on my road bike and
M520's on my mtn bike. I don't think they make the Tahoe anymore but there are many others, some mentioned in the links below. All cycling shoes have a stiff supportive sole and for the SPD compatible ones, a recess which may be covered by rubber, for the clips to go in. The clips come with the pedals by the way (for SPD).
I've included some links below which may be of use.
Asking about other shoes for SPD - recommendations from others
Setting up my cleats and pedals