First, congratulations! Second, hit a few etiquette websites before you start your invites. I say a few, because if you read more than that your head will explode with all the "rules". I'm assuming this is a casual affair and most etiquette sites will have your head reeling with do's and don'ts. Here is a run down of generally accepted answers to your particular questions:
1.) Invite wording for reception only
Mojen and MojenMan McCraftyton request the honor of your presence at a celebration of their marriage Saturday, the ninth of January at seven o' clock Rob Roy Country Club, Tarrytown, Wales
(peeps will know in advance this is just the reception - you don't mention "hey we're getting hitched earlier, but you aren't invited to that." This way, guests will be aware that the wedding itself has already taken place.)
2.) It is never acceptable (in the world of etiquette) to list where you are registered on an invitation. It is commonplace to tell your bridal party and family and they are required to spread the word. While this is stupid and unhelpful to your guests who would care to purchase things for you, it is not what is deemed "acceptable" in the stuffy realm of the etiquette world. But, I would say if this is a close and dear crowd, and you are really humble about it - you could add at the bottom of your invite in a much smaller font "If you would care to purchase a gift for the couple, they are registered at Harrod's."
Here's a couple websites that will help you with all those nagging etiquette questions you never, ever thought you would have to think about:
The Knot - http://www.theknot.com/keywords/sc_221_525.shtml
How to properly address envelopes:http://www.frugalbride.com/addressinvites.html
DIY Templates for things like ceremony programs, etc:http://weddings.shanbritedesigns.com/templates.htm
3.) Where to start on invites? Do you have an idea of the colours or style that you prefer? You could start there, design them yourself and print them out at the local copy shop or on your home printer. You can go as simple (purchase invites from a local shop, premade) or as detailed (design your own, Gocco them, handwrite, etc) as you would like. What is your crafting specialty or interest? You could go in that direction. Just try not to get caught up in all the myriads of options and frippery out there since you have such a tight time table and want to get your invites to people in enough time for them to plan.
There are alot of options out there, so don't get overwhelmed. You have a VERY special and unusual opportunity here of making your invites really personal since you are inviting so few people. So take that into consideration, but take your mental health into consideration first! Good luck. If you need any help, feel free to PM me, I'll do what I can.