A few things I ran into, if I can remember them all.

On the wing, be careful to shim the R2 ribs and remember the 3/32" spacing on the leading edge for sheeting. Looks like it's a bit late for that now, but it also looks like you had it right.

With Epoxy, if some squishes out of your work, wipe it away with a paper towel. The firewall should've been clamped together which would free up your hands to do so. Sometimes a paper towel with acohol helps to thin and remove excess epoxy.

Be careful and work slowly on the wing center spars, LE and TE. Make sure they get a good fit before thinking about glueing. Do the same with the doublers and be sure to clamp them well with the spacing for sheeting.

When you get the wing joined and the trailing edge center and tip TE's glued on, be careful when you're sanding them flush with the wing. Sanding the tops down makes the very edge more like a point and brittle, causing you to have to sand that down a bit, the result: it won't fit in the wing saddle for-to-aft and the ailerons will be wider then the aileron notch

In your pic of the tail feathers, the rudder is upside-down [X(]

If they didn't include it, remember to put the triangular stock between the fuse sides at the end of the plane.

When doing the wing sheeting, careful not to sand too steep an angle on the LE sheeting to make it fit. I did, and there was subsequently a small gap near the top which I had to fill with putty (that worked out fine). The angle is really slight.

When doing the washout, follow the directions carefully, clamp and leave it clamped until you're done. It's amazing that it even works, but you'll be pleasantly surprised when you take those jigs off! I thought that was some of the most contorted and painful construction of the whole plane.

When joining the dorsal fin 1/4" square stock to the fin, be sure it's centered and not really flush with one side. I had this problem...the little tab was flush with one side and off on the other side which would push the v.stab off to one side, albeit not by much. I believe the instructions say to lay it flat when gluing, I guess I'd suggest having the fin clamped and gluing the tab on by hand and centering, perhaps using medium or thick CA to give you time to slide around to center before it's set.

When hinging, take your time and follow the guide, it works well. Cut into the TE's slowly, not too deep at first and make sure the knife is straight, it'll be fine.

Hmm, what else did I learn...

Don't be too eager to finish sand, it'll take off too much wood. Get things rough and don't finish sand until they tell you to cause there's always another piece that needs to be lined up (this might help with the root and tip TE's).

The instructions have good building tips, if you haven't read the instructions as a whole, both wing A and B, cover-to-cover, you should do so. Knowing what's next in the plan can help.

Take your time! Make sure everything's a good fit before gluing, never just glue...someone has a signature on their posts that says something to the effect of:
'Murphy's law says that if you glue without a dry fit, it's not going to fit at all'

When covering, be prepared! On RCU is a review about the p-38, within that there are how-to videos to help you do covering. Watch them! I learned a lot just watching those videos and it helped me a lot. Take your time and read the directions for your iron and covering to get specs about temperatures and what-not.

When mounting the engine, be sure to mark the holes carefully and accurately. There isn't a lot of room for error since the mount holes in the engine won't give if the screw holes aren't perpendicular or correctly spaced.

When putting in the control wire guide tubes, before you join the sides completely make sure the guide tubes don't turn too much and cause binding.

When clamping pieces, use scrap balsa under the clamp heads to spread the pressure and not damage the balsa being clamped.

When putting in the firewall, clamp carefully and firmly. Be sure to wipe away ALL excess epox from the joints. When you put in the nose tripplers they won't sit flush with the firewall if you don't wipe away that epoxy!

Last thing, I guess...when doing the fuel proofing I used 5 minute epoxy with denatured alcohol mixed in to get a thinner, more redily 'painted' viscosity. It worked very well, but I would suggest either using 30 minute epoxy or expecting to cover small parts at a time (5 minute sets at 5 minutes, regardless of thinning).

Hope that helps! There are a handful of pics in [link=http://www.rcuniverse.com/forum/MonoKote%2C_problems_taken_care_of%3F/m_1882404/tm.htm]this thread[/link] from me with my PT-40 if you're interested.

-Dave