Tamiya P-38 kit Painting

Can't address #1 for you, most will do paint work as necessary as they go.

#2 you can either mask off with tape, or stuff soft foam plugs in openings.

#3. Can either spray freehand with an AB of mask with a "worm" of silly putty, or tape rolled lengthwise, sticky side out, paper or cardstock held slightly above the model.  Lots of ways to achive a soft edge if wanted.

More will chime in I'm sure.

I usually don't attach the landing gear until after the airframe is painted. For wheel ells I usually pack the them with dampened pieces of paper towel or something similar. This may prove to be a bit tricky on the p-38 though. There a some delicate pieces of plastic in those main gear wells (I too am building this aircraft). I use poster putty rolled into worms and applied to get the demarcation line. if you spray at a 90 degree angle to the putty, this will give you a softer edge. Reducing the angle will give you a slightly sharper line but still a soft edge. just how I do it and it works well for me.

Paint the lightest color first is the general rule.   I like to use paper masks.  I get a wavy line in narrow areas like the P-38 tailboom by folding Tamiya tape over so only a 1/8" area of adhesive is left uncovered, then cut the wavy line on the folded over section.    Then when you apply the tape it will stand proud of the surface to give a soft edge. Never spray under the edge of the tape, just at 90 degrees to the edge or less.  I like paper or tape rather than poster putty because it is cleaner and quicker for me, and if I want to replicate the exact wave in a picture or  drawing it is easier.   As for the wings and horizontal tail surfaces, on most OD over NG finishes I just spray from one side without masking the other side, but of course the fuselage and vertical surfaces are masked off then. 

Paper or poster putty works good for me in wheel wells and such, and I don't worry about it too much because small bits of overspray can be touched up with a brush.  A good rule to follow is never put any more paint on a model than is necessary to achieve the color density you want.  To get that right you have to know how much to thin your paint and what pressure to spray at, and what kind of paint works best for you and your airbrush.  How far away from the surface you hold your airbrush is also an important factor, if it is too close and your pressure is too high the paint will go on too wet and flow out too much or run, and if you are too far away it will go on too dry, sometimes leaving you with a pebbly effect as the paint droplets will dry before they flow out.  This is especially important when trying to get a good blend as you are trying to do at the demarcation line established by the tape or putty.

Thanks for the information. I am fairly new to using an airbrush. This will be my fifth model using it.

Here is a quick order of build run down since you asked. We all do it differently but it's a base to give you idea of an orderly build. Not all models are the same though.

Assemble aircraft fuselage/wings/ horizontal stabilizer without any smaller parts attached such as pilot tube, antennas/Landing gear and bay doors, etc.

Prime it/paint it/clear coat/decals if you do them/another clear coat/do a wash and weather job/ Clear flat coat/ Attach small parts/ wheels and bay doors/ Canopy if not already attached/ordinance, etc etc.

All the steps mentioned include letting the paint and clear coats dry and cure properly before moving to the next step. I like to put my painted parts in a food dehydrator to dry and cure faster.

Good luck on that build I have on waiting just not quite ready to build it yet.

Unless it's a simple kit, I pretty much do what Tickmagnet said.  I can't tell you how many  landing gear I have busted, just from the weight of my hand while decaling or weathering.  So I generally leave the gear, doors, etc off until the model is pretty well finished.  I paint those parts separately and then attach them, sometimes using white glue to prevent the paint from dissolving and making a mess.

If I do put the gear on before painting, I set the plane on a cardboard box with an open top, so the wings support it while the gear hangs freely down into the box.  

I built this kit last month and waited to paint until it was almost finished. It's easier to install the landing gear when called for in the instructions rather than waiting until after painting as I usually prefer to do. The gear is rather robust and held up fine when I wrapped it with a piece of paper towel and a strip of tape. I used silly putty to demark between the lower color and the top with some masking tape to protect from over spray. 

I always leave the LG off until painting is done.  While I also have packed wells with tissue, sometimes I put the gear doors on with poster tack before painting  If it looks like a good seal, I go ahead and paint.

I have also used poster tack to put on the movable portion of the canopy to allow me to paint the plane before permanently gluing on the canopy.

 

When it comes to masking and painting, spend the 5-10 bucks and get an Eduard canopy mask. It will make your life so much easier when it comes time to paint the canopy. Since I normally use rattle cans (Tamiya's are for the most part idiot proof) so I will mask off the bottoms of the wings as well.  Some will leave the canopy off and mask the painted cockpit with tape and tissue stuffed into the opening. I attach the canopy and go from there. It eliminates a couple of steps and insures that the canopy matches the rest of the plane and no paint gets in the cockpit(if you're using a custom mix, it's noticeable if it's a couple of shades off). 

Thanks, it is on the gear now. I think I will leave the gear doors off and paint them before putting them on the plane. How does this silly putty work? What do you do?

Kit comes with precut masks.

An old article but still relevent

http://www.finescale.com/~/media/import/files/pdf/b/3/1/sillyputtymasking.pdf