I know they had Pz I's available, probably some Pz II. Probably all the Pz III, Pz IV and Pz(38)t are with the divisions. Not quite all, but no useful reserve
Yes the reserve is roughly the same as training vehicles and kit under factory repair rather than an available material reserve. In terms of production the OTL numbers will be wrong. The Germans demobbed factory workers very quickly after the BoF and started to change models. But in terms of production 0 P1 per month, around 30 P2 30 P38t, 60-80 P3, 20-30 PIV and 10-20 Stug and 30 armoured cars. One issue for the Germans is whether they switch to 5cm guns for the P3 which will reduce the numbers produced.
And between 1-2000 trucks per month. So if a PZ division has lost its soft vehicles its a months production to remotorise it or you end up demotorizing other things and have to replace that transport with horses - which are useful in agriculture or porters.
Second issue available for use. A lot of vehicles will have some form of damage and amongst the items being lost will be the truck borne repair units ( also signallers, medics, artillery specialists who won't be with the panzers and are not equipped to fight past the inevitable unsuppressed machine gun). But without the repair units lightly damaged equipment will be unavailable, Simple things like are code machines and code books destroyed? because they have to be reissued, and maybe men trained, the kit from the bridging units replaced and all the while men fed and ammo supplied.
Not to mention the loss of trained infantry and their kit.
But the general situation after a week of the war and 3 days of intense fighting - its difficult to criticise French reaction time given its 3 days and you really only know what's going on half way through day 1 of the major offensive
But the end result is of the 10 available Pz Div 6 are combat ineffective for some time. There may be working tanks but not so much the Arty, infantry, support arms, 1 is understrength to begin with and 2 are recovering from meeting the Cavalry Corps. The Motorised infantry are not much better off, they have been frontally assaulting entrenched French infantry and if you go ahead regardless of casualties you will be losing a lot of junior leaders. Overall not high losses but in the specific units engaged probably debilitating. OTL GD regiment had 25% casualties in the fighting around the Meuse Heights 15-17 May. Thats likely to be a minimum for the attacking units for 2-3 days fighting if they are pressing the attack.
The highest daily rates for the campaign were around 4000 per day but most of the German divisions were barely engaged average 1000 casualties for the whole campaign. So if we call the OTL campaign one month the absolute minimum would be around 30k KIA 100k WIA ( of which about half you get back in three months) and probably much higher, say 10k MIA. Which are comparable to July 41 in Barbarossa which is the most intense of the initial campaign. Of which 80-90 % would be in the infantry.
As to what the Allies will know, immediately not much but POW debrief is a thing and the will eventually get a good picture of the German system but not tomorrow and maybe not next month so the allies are unlikely to switch over to major offensive action right away because they don't know how thin the German reserve is and they do know what their production rates are so with another 3 months production the British will have another army in the field, no materiel losses from Dunkirk to replace its all new issue. The French will have replaced their older tank inventory and so forth. Smashing the Meuse Bridgehead or the relief of Fortress Holland is another matter, but smashing really means getting into artillery range. For the Germans that includes battleships bombarding the Dutch Coast.
The other factor is the panzerwaffe as a maneuver element has failed. It cant just refuel and charge again in the morning, and by evening the French will be closing the gaps, digging deeper, laying mines and so forth. By the next day other divisions will have entered the line and the battered formations be reorganised. By the time the the panzers are ready the allies will be dug in wired in and you can't go around you have to go through what you need is a Breakthrough tank which fortunately the Germans are working on be ready by 42 at the outside.
Luftwaffe position is far worse. Either the allies have free rein over the battlefield or you have to fly - and Essen is 150 miles from Antwerp which the allies hold and there is no reason for the main allied forces to have withdrawn from Brussels. Thats a reaction to the OTL Offensive now the Dyle line is holding, so Leopold has no reason to go surrendery negotiate for free stuff and food for his army and population yes. The Ruhr is in range of fighter cover from Belgian airfields and most of German production in range of unescorted bombers from France.
Division commanders in all the Allied armies have more limited freedom than you might imagine compared to the German. Because they are using Corps assets. The French OTL slightly less so than the British but I suspect thats a function of the advance to the Dyle line and putting the Corps HQ forward with motorised elements so they can plan the defence. The BEF 1 corps for example has 3 MG Bn ( plus 3 more from GHQ plus GHQ engineer bn) CCRA with 2 field 2 medium 2 light AA regiments, CCMA ( medium atillery) with 2 field, 3 medium, 1 heavy 1 super heavy regiments a separate survey regiment and corps assets for troop transport, ammo columns in addition to the divisional equivalents.
The Div commander may be the planner for an action in his sector which may be the corps main attack but they are far less autonomous than the German equivalent but do have access to more firepower. If you want a picture look at the 100 days at the end of WW1 or Alamein, Mareth Line, Diadem, Normandy and so forth. One division - backed by Corps assets attacks draws in german reserves, Stops after a fairly short time, new division attacks on a slighty different axis using the same corps assets more reserves sucked in Another corps does the same with its divisions, The First corps repeats Another army chimes in etc. So for example the Canadian Corps in the 100 days fights over those 95 days the battles of Scarpe, Albert, 2nd Bapaume, Arras Drocourt canal, Havrincourt, Epehey, Canal du Nord, 5th Ypres, Sr Quinten Canal, Cambrai Coutrai, Selle Valenciennes capture of Mons Sambre Passage of the Grand Honelle. or one distinct action every 5 days. You get the same thing in 44 - plus XXX corps.
The Other part of the picture is the failure of the German army to do anything like this, they go around or specifically try ( and normally fail) to break through after extensive preparation. The highest casualty days mentioned above were both during Fall Rot, With the Exception of Sedan the French don't break disintegrate, fall apart or otherwise panic much at all.