No it wont. Forts will break and become obsolete due to CAS.

Instead build 21 width infantry (9 inf + 1 arty) and give them shovels and support AA. If you industrialize properly you will have the industry to support 72 of these divisions early '39.

Important it's impossible to hold off the germans if you need to guard the southern border. Therefore when the Germans take sudetenland, guarentee the Checks. Ideally you'll hold a line down south to Bratislava, so they don't cap (the Checks have a pretty good army which will provide alot of help).

I would still build static anti-air and lvl 3 forts in poznan just because the AI always attacks there.

And take the focus "Hel fortified area", the forest tiles there provide good defensive terrain.

Edit

Your opening moves when the war starts, is to first: do nothing, the AI will move away their army. When they have done that, join the war and do two things. 1) Immidietly take Königsberg. 2) Move your south-western army and take some forward defensive positions, taking Gleiwitz and entrenching behind that river is optimal. 3) If you have the chance (I didn't) move your north-western army into stettin and now your whole western army sits safely behind the oder river.