2. The Slovaks know that this is their only chance to secure their independence/home rule after the war - jump in too early and the Germans squash them, too late and the Entente treat them as an Axis power and puts Beneš back in charge.
Do Germans however have what to squash them with? Uprising in occupied Poland, Hungarians declaring war, Brits pushing towards Poland, French towards Austria and Czechoslovakia. OTL in 1944 squashing took Germans 2 months and Slovaks were fighting mostly with 1939 weapons and more then half of their army gone. Here Germans do not have much new weaponry. And as I said OTL Germans had problems to find enough men power in Protectorate to sent against Slovaks. If they strip men power bare in Protectorate, it is still not enough and there is risk of Czech Uprising then. Protectorate had small so called "Government army", 12 Infantry Battalions plus there was strong Czech Gendarmerie which was in majority pro Czechoslovak.
Slovakia as such could mobilized app 100-150 K men. They did so during war against Poland but used only 3 division and Rapid Group. Definitely they had enough weapons from Czechoslovak stocks to equip app 125k men. In their peace time OoB were 9 Infantry regiments, 4 artillery regiments (weapons for more and some 587 artillery pieces), tank regiment (17 OA-30 armored cars, 30 tanketts TC-33 very obsolete, MG armed, 27 LT-34s obsolete and 52 LT-38, OTL in 1940 10 LT-38s and 21 LT-40 were supplied, I somehow doubt LT-38 will be supplied with German situation, LT-40s could happen though as they were originally ordered by Lithuania). At that time Hungarians had just slightly larger amount of armor!
As to Air Force was probably most obsolete. Here they will very unlikly got any Bf 109s. But still had some 71 B/ Bk-534, 73 S-328 and 14 A-100 plus numbers of training aircrafts.
As such not very strong force but not really something which can be smashed in day or two. Even if Germans put their shit together very quickly, still they will be not able to occupy more then western parts along Vah river and Bratislava. Heck due to situation Slovaks may even get some Hungarian air support. It will be in Hungarian interests Slovaks hold. I wouldn't be surprised if after Hungarian declaration there were some secret negotiation with Slovaks in Budapest.
3.The Entente have probably denounced the Munich agreement by now, and the Vienna Awards are something they will want to discuss at length. What they don't have is a firm policy on what they should do instead, having been concentrating on other things. The Slovaks have at most a few weeks to create facts on the ground before it gets to the top of the to-do list...
With few weeks to jump in it is plenty of time. Due to Hungarians jumping in they can even mobilize as to precautions. However Tiso would be smart if he did it right after Hungarian declaring war. With mobilized army he has much more room for maneuver.
The Hungarians have armor, and the Polish Home Army probably doesnt ... and going to where the opposition isn't and the Home Army is strikes me as a good idea for the Hungarians.
At the time Hungarian armor was app 65 Italian tankettes L3/35 and some 95 Toldis.