You don't need to well, "baby", a baby hand-fed budgie as it should be able to adjust quickly to change at this age. In the wild, they basically jump out of their nest and immediately face the world, which is much more to take in than a cage and being handfed it will already be socialized to humans and view you as a flock.
I only have cages with those doors and have never had an issue. Almost all cages have those doors. Just secure them with a clip when open, don't let them stay open by their own weight, as they can fall. Likewise, my budgies quickly learn to climb the vertical bars.
The cage is small as a permanent cage but perfect for a baby bird.
Dowels are perfectly acceptable perches when used in conjunction with some other types for variety. I use dowels in every cage, combined with a varying assortment of natural branches, big and little swings, ropes and flat wood perches. Dowels don't hurt bird's feet, it's a misconception based on how if a bird lives in a cage with nothing but perches of a single diameter it can develop foot problems due to a lack of flexing.
I don't think you need to do anything special at all, but if you want you can set a little shoebox on the cage floor with wood chips or hay inside to give the baby a "nest" that it can leave on its own when ready and sleep in at first if so it chooses.
Wing-clipping is not necessary. I have tamed fully flighted budgies with clicker training in a couple of days. A hand-fed baby should already be tame and come to you on its own.