Hi Piotr.
Firstly. Balsa is a 'hardwood' but is actually very soft and extremely light. It is used widely in the Model flying fraternity due to these characteristics but I would not use it for coach construction purposes, apart from internal panelling, seat making etc. due to its lack of strength.
For coach framing I use 3mm square hardwood from my local model shop (or online). Obeche I think.
For making rebates in this stripwood for glazing and panelling etc. I made myself a simple jig from workshop scrap as the following drawing tries to show.
I then slid a strip of 3mmx3mm wood (yellow) into the slot and carefully planed with a shoulder plane lying on its side until just touching the top guide on the jig. This cut a rebate 1mm deep and 1mm wide.
What doesn't show, is that there is a thin ply stop glued at the far end of the jig to stop the strip sliding right through it.
Take care when planning not to cut sideways into the top guide as this will take out more than 1mm of wood over time. My guide has been replaced once already and I need to replace it again as it has worn away too much again.
One problem I did find was that the 3mm strip could be a little over size in some cases and not fit into its intended slot on the jig. I was lucky in that I had way too much of the strip wood anyway so could pick and choose which bits I used but it is worth bearing in mind to buy more than you need. I also found that although I was cutting the strip into 100mm lengths before rebating, the thickness along the strip may vary, so I could use some bits from the original length if maybe not all.
If you need a strip for glazing on both sides, make one rebate then turn the strip around to rebate on the other edge to end up with a 'T' section.
On the subject of weathering, I ensure there are no sides and edges that have not been painted or varnished. Even the glazing rebates discussed above are primed and glossed with the rest of the coach sides before the glazing is glued in place. After a running session all of my rolling stock is brought into a warm room overnight to completely dry.
Sorry to disappoint Piotr but the station buildings are not mine I am afraid. Being a member of the Association of 16mm NGM, here in England I have the very enjoyable pleasure of visiting and running on other members lines in the South Leicester area. That particular station is on the Brixworth and Lamport garden railway.
David.
David T.