As a kinda-sorta native that has studied such allohistorical scenarios closely, I will only say this :
Czechoslovakia defeating Germany alone ?

HELL NO !
I think this is a perfect sample of the thinking that brought France and UK to appeasement. Look how Germany is big ? Look how Czechoslovakia is big ? The latter has no chance, Hitler would prevail.
But there are few points that are usually not taken in consideration :
- Fall Grün asked for sneaky attack to prevent Czechoslovak mobilisation. However the mobilisation was completed with 1 million soldiers ready. Germany had no attack plan for a case of enemy in a full strength.
- Hitler was asking for an attack to happen no longer than 10/1/1938. Wehrmacht was not ready for that date even if instead of Munich talks they had a week to get to positions. They either had to postpone the start (unlikely with Hitler at helm) or face prospect of attacking with incomplete army.
- There was no mandatory army service in Germany in thirties, meaning a large amount of men had no training. Germany needed time to cope with this, Wehrmacht of 38 was no Wehrmacht of 39 in Poland or even one of 40 in France.
- German logistics was a mess at that time. All the transports to support attack from South needed to go through Linz, making it ideal target that would hamper the German attack seriously. Czech transfer routes were much shorter.
- There was no way around the fortification system. Germans had to find a way through the bunkers. They would find it eventually but their initial casualties would be enormous and progress would be minimal. Those dead soldiers would be of no use in further battles, highlighting the above points.
It is believed that Czechoslovak Air Force was no match for Luftwaffe. If the war started in 10/1938, there are few additional points to consider:
- Luftwaffe was short on pilots. Many of them had just a basic training, no advanced fighting etc. They would operate over enemy territory, so any shot-down would mean the pilot is lost. This proved to be an important factor in Battle of Britain.
- Bf-109 monoplanes were just recently introduced. There were multiple versions of them (B/C/D) making the task of keeping them in service extremely difficult (lack of spare parts, experience of mechanics), pilots were not yet trained for battle on monoplanes and wet weather with muddy airfields would be bigger trouble for modern, heavier planes.
- Early Bf-109 versions (especially the Bf-109 B, which was the most frequent one in 10/1938) had weak engine and just two machine guns, so it was actually underpowered and under-gunned compared to Czechoslovakian Avia B-534. They were slightly faster, but the difference was not that big.
- Luftwaffe was still in older system. New one, for which it was praised in WW II was only to be introduced in Winter 38/39
- Biplane fighters (Arado Ar-68 and to some extent even Heinkel He-51 - former fighter in ground attack role) were still part of front line Luftwaffe. If there were any troubles with keeping Bf-109 operating, biplanes would be still important factor. Arados were inferior to Avias
- Weather was shitty, and plan to destroy Czechoslovak Air Force on the ground was prevented by distributing the planes to field airfields.
- Germany had very limited supply of bombs, ammunition and petrol (in that order). If they depleted the resources, there even might be a Czech air superiority after a couple of weeks, however unlikely it might sound.
Those are all quite important factors, yet most of the people tend to study map, see how Germany is big, take their success in 39-41 into consideration and proclaim them victors in 1938 too.