Newbie Q(s)

Before starting a build, most everyone will wash all the sprues and parts with warm soapy water (dish soap) and rinse well, let air dry.  Sounds like you still have some mold release on the parts, washing will get rid of it.

I personally will lightly scuff everything with a fine (gray) auto paint scotchbrite pad.  If I prime, I'll finish scuff with the same again prior to color.

I use about the same ratio, seems to work for me, others will use different mixing ratios and different paints.

Haven't had an issue with paint peeling off when masking for other colors, either primed or not with either Tamiya or Model Master acrylics.  I will prime more just to cover filler and check for acceptable filler, low spots, visable seams, etc., and have one color to have to cover rather that a couple of varying colors that may take more coats, depending on the color.

Once you get the paint to your liking, spray a coat of gloss clear overall, then decal.  If you are going to weather, do it now, then you can give it a coat or two of flat clear to seal everything and give it the flat look of a warbird.

You’re doing everything right in the basics. The main root of this issue is that Tamiya acrylic paints are not overly scratch resistant. I’ve been using them since 1984 or so, and they never have been. Especially before they cure. Tamiya kits, unlike say an early ICM kit, do not arrive at your home slathered in mold release agent. So that is not a likely factor. Tamiya paints ( as opposed to Model Master acrylics) do have very good adhesion properties on bare plastic, so priming is not a necessity with them. But priming will not hurt either. And unless your fingers tend to be quite oily when you are modeling, leaving some of those oils on the plastic as you work on said model, you are not likely to need a wipe down with some sort of agent such as “Plastic Prep” before you begin painting sessions. Your mix ratios of paint to thinner sound perfectly fine, I often use the same.  

As far as clear coats go: a gloss clear coat is a great idea before decals, followed by whatever final topcoat the finish requires after the decals and washes are on- flat, satin, semi gloss, or gloss, and then any final weathering such as pigments. Pigments have a tendency to get toned down or disappear under any sealing top coats, which is why they are best left until last.

It's a misunderstanding that additional coats will improve adhesion. The first coat bonds to the substrate, or not. That's it. If you were to prime with white and then add two or three coats of gray, and have tape pull the paint off, look at the backside of the paint on the tape. It'll be white.

Some Tamiya acrylics bond better than others. I have a hard time with their Flat Black, but most of their colors seem to stick pretty well.

Priming is always a good idea. Not a must, and some paints will self prime just fine. Others won't, plus priming has other benefits. It provides a good way to discover flaws prior to applying finishes.

I've never really had a problem with paint un-bonding from other layers of paint.

All the above from goldhammer, stik, and bill are spot on.

I would only like to mention that on my first kit back from hiatus 5 yrs ago, after having spent months on a 1/48 model airplane, my unprimed paint job pulled up with the masking tape. I'd prefer that not happen again, so......

I have primed everything since and never had a problem with lifting, scratching, or adhesion.

Just my (this is with acrylic paints, btw)

Sounds like everyone has covered this good. One thing I would like to add is I do wash everything in a small tub to keep anything that might get knocked lose from going down the drain. After assembly and before I start painting I will wipe the entire model sown with rubbing alcohol it evaporates fast and removes any oily finger prints try I may have left also while painting I'll wear cheap disposable gloves from harbor freight to keep from getting any prints on it while painting. Hope to have helped some.

Thank you all for your advise, sounds like I’m on the right track, lessons to be learned for the next one, will try priming to compare the reaults.

the challeneg is seeing all these amazing scale models and the experience to achieve those results is extensive, I want to get there but it’s going to take time but I’ll get there quicker I think with so many people willing to help...

cheers from