Please do bring the MP40... If it's windy there you might find you full-auto rather than single shot. It's quite open to the elements in some areas.
Other than that I can't help! 
I will hopfully be attending this as well, and this will be my first time as a German, I already have a AGM MP40 and for a laugh I will be bringing out my D boys K98 with all of three working shells ( one always misfires 
), but the rest of the kit I am going to have to start from scratch as well.
"Will you stop talking about the war!!"
"What, you started it!"
"We did NOT start it!"
"Yes you did, you invaded Poland..."
Harry, it's impossible to get a decent K98 unless you're willing to spend quite a few notes. Your choice is either a Tanaka gas-powered one (£540 at Wolf Armouries, plus £50 per mag), or to get someone to make a custom springer using (say) a JG BAR10 internals fitted into (say) a Dboys K98 stock. If you can do that sort of work yourself, then that is ultimately cheaper - I paid a friend to make me one. The parts alone would probably cost £300. See this thread for details on how others have done this. viewtopic.php?f=13&t=1613&start=0
For a P38, I'd recommend the Maruzen.
You've got nothing to ein, zwei, drei, vier
How's your shooting skills?
If they are as bad as mine, stick to the MP40, at least you can lay down suppressive fire for someone who can actually hit a man sized target at 30 paces! 
To the tune of "Mademoiselle from Armentières"
Napoleons army ran away, As you do
The guard stood firm for Frances Pride, As you do
They said the guard will stand and die
But we heard what their Colonel cried
It wasn't pretty I tell you.
Resistance is fertile
The MP40 is an excellent weapon - reliable and pretty accurate for an SMG.
You've got nothing to ein, zwei, drei, vier
Do the hop modification and fit a decent barrel to the MP40 and it can shoot really well, without costing the earth. I've had 40 metre kills with mine.
When I want your opinion - I'll tell you what it is!
I think your best bet for a rifleman is what Steiner Suggested. Many have made custom Kar98 Springers from Chinese clone guns and have worked really well... I can testify how straight they can shoot when done right! 
hehe
As for kit, if you're looking for DAK, have a look at the DAK kit guide for Kasserine, plenty of folk have put up links there. May I suggest you get as many items of kit to begin with which will be ok for BOTH DAK and North West Europe impressions, as you'll get much more use out of the kit in the short term.
