Nice work so far Ben.
As to weathering, well you will get a lot of different advice on this. From Me:
You need to apply the decals before starting the weathering process. Before adding the decals spray the vehicle with some light coats of Future Floor Wax to seal the paint and give you a smooth base to add the decals. This will help stop the decals from silvering (a milky grey shine from air trapped under the decal). Future is water based so will not effect the enamels - don't thin the Future though. When the Future is dry add the decals and then once the decals are applied and dry, use a mix of 70% Future and 30% Tamiya Flat base and spray that in light coats to seal the decals and restore a flat finish. Allow that to harden for at least 2 days. This will allow you to apply washes.
A wash is paint that has been thinned up to 95% depending on the effect you want to achieve. The idea is that the wash is applied with a wide bristle brush, and being thin, the colour will run to the grooves, and edges of protruding parts, but will not gather on the flat surface. I use artists oil paints thinned with white spirit or enamel thinners myself, but others use artists acrylics, etc. Basic colours to use are Raw Umber for a dark wash, Raw Umber and Yellow Ochre mixed together for lighter coats, and Burnt Sienna for darker rust streaks, petrol spills, etc. The oil paint should not effect the Future Floor wax finish.
Apply the wash sparingly, but if you apply too much just use some kitchen towel to soak up the excess straight away. For areas like joins between hatches and mounts, etc, just add a little black to the Umber wash and using a fine pointed brush just touch the brush to the join so the paint will flow around the join using capilary action. Leave the wash to dry for 48 hours.
Next is dry brushing. For this you can use artists paints or enamel paints. I find acrylic paints (Tamiya, etc) don't work well. The idea of dry brushing is you scoop a little paint pigment (don't mix it, leave the runny medium behind) onto a piece of card, and let the excess medium soak into the card. This leaves just the pigment colour. Using a wide flat brush, dip the end in the pigment and then wipe off most of the paint on a rag. You need just a hint of paint on the brush. Then gently brush the tip of the brush over the model so that the colour transfers to the raised detail on the model (ie the rivets) after a few passes. The idea is that it will be added subtly, so one pass should not deposit the paint or result in streaks.
Start dry brushing with the base colour, as the future and wash will have darkened that. Then lighten that colour (yellow works best for OD) and dry brush a little more gently with that. Keep lightening and dry brushing the detail in ever lighter strokes. The idea is that the really light colour should be on the top of the detail, with gradually darker shades going back closer to the surface.
This is the basics, and you should start there. When you are comfortable with that you try applying pastel chalks, filters, shading, wear and tear etc. See this link for details on these methods.
http://missing-lynx.com/rareworld.htm