surviving as chzechoslovakia can be done very reliable if you have 3 things:
1st all sudetenland fortress NF
2nd at least bulild lvl 5fort in northern Zaolize and lvl 3fort most western porvince of southrn slovakia, as here you will only get a +2 fort from poland line(zaolize) and 3+fort form hungaryian line(southern slovakia)
3rd an ally, USSR or GB/FR are great depending on if you gop commintern or democratic
if you lack the ally it is still possible but much harder, if you lack any of the forts your dead meat from what i know
if your lucky, very lucky hungary will enact the rome protocol and italy will defent austria from anschluss, but dont count on it even after hungary joined with italy, italians often bugger out and cower befor germany instead of fight for glorious death
if your not extremly lucky but somewhat WT is above 25 so UK will guarantee you and you may have a proper ally from start of war which helps reduceing the amount of german division drastically(50-75%) on your border
if evrything goes as it should not and hungary joins axis befor of shortly after the sudeten crisis you should be ready with lvl5 or better forts to the hungaryan border, but this is useless as long as hungary is neutral or defendiong austria so always look what they do in terms of NF
for what you can actially do to survive is relativly much
most important is dig in with as much entrenchment as possible, i usually use engeneer brigade, devensive FM and trench warfare for more then 40% entrenchment
build at least some fighters, 1 factory is just enough to not loose to much defensive fro air supiriority
also consider AA batalion, as there reduce air superiority by about 8% flat (so from 30%->22%) and add minor piercing (about 13-14 piercing for division) so you can pierc the light tanks without expensive AT
for NF there are some very usefull ones beside the fortification ones(which at up to 1.2% manopwer, around 180k soldiers) very important are the idustrial and the political branches, but imo to do the strategic decision and the military stuff is just not enough time, remember you have ~2.5-3.5 years depending on rng/historic befor war will break out
i usually go for political decision followd by fortification1 and the idiolegy of choice(dem/fas/com) and then fort2 followed by industral/skoda works untill i can advance my ideology choice and fort2, fort3 will only be taken once germany takes (NOT finishes) anschluss because that is the queue 140 days for war
if you go democratic the beacon of liberty and defensiv preperation are of utmost impotance once you have the democratic supoort needed ( free 5% techbost, 10% def and 3.5% manpower for only 84 days)
the last of skoda work equal acceys gurantee is almost useless though at least in the opening and divided nation is managable since you get 1.2% manpower from fort NF and dont plan to loose prag i hope so industry does not need to be finished by war
usually japan has attacked chine before anschluss so guarantee of UK should be present but dont count on it, same with romania/jugoslavia/hungary
while jug/rom may be possible allies they fail hard, jug always and rom whenever they border GER
hungary when defending austria often folds within 70 days so you have to improvise on the southern front as you now have a vast and almost unprotected belly for GER to just dive into
also once the sudetenland is breached, as in 2 or more provices have fallen and have at least 1 german division with more then a slither of org you are close to dead as you will most likely not get the provices back, lvl7 fort and all, and they will just funnel tanks into prag for an easy fast deathblow, and zaolize is a very likely canditate for this since as mentioned above you dont get free forts here that are worth anything, western slovakia has a river but is also under threat
for military i go cheap and resilliant, 7/2 inf with engeneer and aa, not even suport art as they cost precios org(~8%) and production(~11%) but offer only ~15% firepower, same with mountaneers as they cost 40 more small arms(~15% cost of division) but offer only ~8% combat ability in mountan 4% in hills when defending
similar with tanks/mot to high cost for to little gain if any
for strategy think of turtles, wait for GER to attack and hope hun does not join them, but always be prepared for it
once allies/comintern go for germany you will most likely succed if you still own all your provinces and can deflect the attack form south, if you switch to slightly less turtle mode you may be able to snatch sachsen and ober/unterschlesien from the germans but that depends on luck and ability
and if you die just think about which decision killed you and restart, my first czech game i did not build any fort in zaolize and was dead within 2weeks outflanked through that province so i started with there and imporved to this wall of text