Sewing Shirring for stretch in doll scale? lining garments?

The answer to question 2 is simple. You make the lining as an entire white dress, then attach it at the ends of the sleeves, the collar, and the back opening, then bag the garment out.

 

About the shirring.
In your picture it look like it's simply a number of channels between the outer and lining layer with elastic in them. That is perfectly doable in doll scale as long as you make sure the fabric is not too stiff. It can be done by hand, but it would take great care to do so that it looks neat.
The other common way to do shirring is to use elastic thread either in the bobbin of the machine or sigsag over elastic tread. These can be done small if your machine can handle it, but it's a lot harder on short seams.

Anything with elastic in it is prone to aging badly, so do keep that in mind if you are making things for other peoples dolls.
With the first method it's possible to replace the elastic when it dies, but not with the second.

 

I'd say it dependy on why you need several sizes in one garment.
If you are doing it for your own dolls and simply want the garment to be shared between them, then I think the elastic channels are a good enough method. You can replace the elastic yourself whenever needed and you likely only need to do so every ten years or so, depending on elastic quality and enviromental factors (heat, humidity etc.). It's not a big deal.
If you are making things to sell and want to make garments that fit a number of dolls because of that, it gets a lot trickier because you won't know what size to optimize the garment for and you don't know how much work the future owner is willing to put in to make it fit. You will also likely want a product that lasts for a long time with as little maintenace as possible.
Some doll clothes are sold with an exagerated overlap in the back so that snaps or buttons can be moved into the correct position to fit the doll. This works well enough for small size changes and it's easy enough to do that anybody can do it (or at the very least is likely to have someone in their life that can do it for them) but it doesn't accomodate many sizes at once.

Regardless of the method, there is no way to make the fit perfect for every size in just one garment. You are going to have to decide on an optimal size and tweak it from there, accepting that the further you go form that size, the worse the fit will be. For something relatively simply fitted, like a lolita dress, that may not be the end of the world, but something more structured, like a ball gown, there may be problems. The last thing you'd want is a garment that a lot of dolls technically can fit into, but that doesn't fit any of them quite right.

 

The main fit problem will be that the difference in size is at the highest point of the bust, in other words in the space at the front of the bodice, while the size adjustment (elastic panel, movable/multiple fasteners or whatever is used) will be at the center back. It's not just a matter of circumference.
A fitted garment is a three dimentional thing and simply pulling it tighter will not change the overall shape, too much space in the bust will still look baggy if there is nothing filling it out. All pulling it in will do is making the back narrower. This will also pull on sleeve openings, shoulder straps, necline and any other features the garment may have. If the waist is not being pulled at the same rate this will also create a diagonal pull on the garment that may cause buckeling or pulling of the material in ways that are the hallmarks of poor fit.
Again, for a farily simple fit, like that of a mostly tubular bodice with narrow shoulder straps or similar, it may still work. It's worth a try. And after all, Many old shool lolita dresses had their main shaping done by the waist ties alone, it's not a fashion always tighly fitted to the body. Tricks like adding decorative lacing to distract the eye from an elasicated back can also help a bit and is commonly seen in lolita dresses. The waist ties fill a similar function, as while they do often create a little bit of baginess, they do also make sure that the waist itself is smooth and pulled in the right direction.

 

I have some doll dresses with a panel down the centre back that are shirred with multiple lines of shirring (not inserted elastic - it's sewn with elastic thread in the bobbin of your sewing machine, and regular thread on top) that work well for accomodating different bust and body widths.

It looks fine in doll scale - personally, if I were doing it, I'd sew the parallel lines of shirring closer together for doll scale than I do in full sized dresses, just to make it look more in scale with the doll, but that's a matter of personal taste:

YouTube has many vidos showing how to use shirring elastic - I just did a search on "how to sew shirring elastic by machine" and found loads of them.

Teddy