im in the exact situation as you are, my small modelling budget means i 100% hand brush my models from base coat to weathering. i build mainly 1/35th military and work with Revell Aqua Acrylics for painting and AK Interactive Enamels for weathering. i am, however no means an expert (3.5 models done so far) but here are some tips (in more or less chronological order of the modeling process):
NOTE: sorry for the long text ahead
-clean the parts in soapy water to remove any mold-release agent
-build the model in easily painted sub-assemblies if you can. in some cases, some places will be impossible to reach with a brush (the complex suspension on the Revell Fuchs i built for example meant that some parts were left unpainted). my way of working is to keep a brush during the build process an paint just plain water onto the parts to see if the brush will reach before actually gluing the part. if it doesnt reach, i leave the part aside to paint and attach later
-use a primer. even one from a spray can will do the trick. this turns all the different colored styrene, resin, photoetch, etc. into one continuous base coat to work on. it also helps highlight any imperfections in the model allowing you to rework them. grey color works great in general but white will be especially good for lighter colored vehicles
-know your paint. before attempting to paint, play around with some of your paint. try different thinning ratios. try out your brushes. remember there is not one be all, end all ratio to thin paint. quality varies between manufactures and even within batches of paint, and environmental conditions can affect the paint as well. practice on some spare parts or a really cheap model to get a feel of how your paint performs
-have a good selection of quality brushes. cheap brushes will leave you frustrated and with unsatisfying results. i use the Mig Abteilung 502 series of synthetic brushes. they work great for me and are not as expensive as natural sable brushes. also keep a nice assortment of sizes, at the minimum you will need a small round detail brush, a medium sized round, and a large flat for larger surfaces. you could slowly build up your collection as you need them.
-if you paint with acrylics, use a wet palette. either DIY or one that you purchase, a wet palette will keep your acrylic paint from drying out to fast and allows you to work slowly. it also keeps you from having to re-thin the paint as often
-coming from the previous tip: BE PATIENT! when brush painting, its important to be patient. to prevent the dreaded brush marks, its important to build up light coats of paint rather than just slathering it on. this is where the wet palette comes in. i once had to do 4 entire coats of base color to paint a model but the result was smooth.
-allow the paint to dry. usually brush marks are a result of overworking the paint, i.e., repeatedly passing the brush over as it dries. paint will normally "self-level" as it dries, but if you overwork the paint, the brush marks have no time to "self-level" and you get the dreaded brush marks. also, if you need to hold the model while painting, if the paint is still wet, youll leave fingerprints. so again, be patient, it may take days, but its worth it.
-clean your brush often. paint will work its way up into the bristles of the brush, and if not cleaned, will dry up and ruin the brush. so have a small pot of water/thinner and every now and again, take a moment to rinse out the brush. and when the painting is all said and done, clean the brush well. invest in a brush soap or cleaning liquid to remove most traces of paint.
-if you decide to choose enamels for weathering, keep a separate set of brushes for acrylics and enamels. brushes used in enamel paints should not be used for acrylics unless thoroughly cleaned.
-ENJOY IT. for me, brush painting is almost like meditation. keep yourself relaxed and enjoy the process. sometimes i even put a movie on to watch or have some nice music in the background. we may occasionally get stressed out while building/painting, but remember to have fun, because thats what this hobby is all about.
sorry for the long text, but i hope this may be of help ;D please dont hesitate to ask questions about anything i posted here if its unclear
