In my setting, I have created a technologically innovative faction which seeks to utilise various past technologies, namely, aircraft.
For context, the setting is a post apocalypse type setting following the dimensional collision of Earth and a fantasy world, which fried most electronics and resulted in the collapse of modern civilisation. It has been 98 years since the event, and various societies and groups, changed as they are, are beginning to return.
This brings us to the faction, a joint coalition of humans and gnolls which are defined by their utilisation of technology on a wide scale, in comparison to some of their more medieval neighbors. Of particular note is their attempt to establish an aviation program. This is facilitated by their possession of an invaluable old world treasure: A vintage B-25 bomber, an aircraft renowned for its durability, ease of maintenance, and, most importantly, forgiving flight characteristics. Due to it being a collector's item pre-collapse, it was maintained to a near-new standard, and was stored in a hangar in ideal conditions until its discovery. Accompanying it were various manuals detailing the maintenance, engineering specifications, and instructions for flight.
They have also acquired several high-quality examples of common, simple to maintain aircraft, namely the Cessna 172 and Piper Cub, and numerous spare parts for them.
I chose propeller aircraft due to the belief that, despite their older status, they will be infinitely easier for a industrialising society to restore to a working status than modern jet turbine aircrafts, which are also are largely disabled due to the scrambling of complex electronics.
Whilst I feel it unnecessary to deliver too many details, I will add what may help with the question:
They actively seek out information and technology which will increase their standing, and have placed a bounty on aviation-based information such as manuals and textbooks. They are not working from scratch, and have no intention whatsoever of doing so.
They have engineers, machinists and mechanics, albeit trained to an inferior quality than modern equivalents, and are actively seeking out and training experienced individuals.
There are several individuals trained as pilots, though mostly in theory, with the exception of two who have achieved flight in Piper Cubs.
They have industrialised to the extent of having mining operations, and are capable of producing iron and steel in moderate quantities, machines such as small arms, having reclaimed various engineering apparatus such as lathes and milling machines, and have a working, small scale foundry.
Population of roughly 6,000 EDIT: As one commenter pointed out, this may be an unrealistic population number, and thus may change
They are aware of the existence of gasoline and its importance to the operation of engines, and have refined it in small quantities. They currently lack a large oil refinery/drilling operation, at least to the point of consistently producing aviation gasoline, but are attempting to create one, and will likely do so.
Lack of trucks or other motor vehicles, due to the preceding point.
Essentially, my question can be boiled down to three points:
Would aircraft be airworthy following 98 years of storage, regardless of their pre-collapse condition?
How realistic is a post-apocalyptic, industrialising society maintaining the logistical and technological conditions necessary for (limited) aviation?
How valid are my choices of aircraft? Under the factors underlined, would the faction be capable of maintaining larger, more complex aircraft, or am I severely overestimating the ease in achieving flight again?
NOTE: I feel I should specify that in regards to the B-25, they do not intend to constantly use it, it is more of a propaganda piece/flagship, meant to show the "technological mastery" effect the faction is trying to project. I had an interesting idea that they may frequently repaint it, so that it seems they have many more than they actually do. They do, however, need it to fly it in combat at least once, so that it is known that the thing exists. The majority of their air force would consist of less resource-intensive craft, like salvaged bush planes, and thanks to your very informative and helpful comments, various wood and cloth WW1-era biplanes, as well as several zeppelin-type airships.
Edit: Thanks to @schmuddi for the suggested edit for the grammar and formatting, it was very good.