They seceded through their own properly seated governments.
They didn't have to recruit an army 10 times larger than the Union army.
They did when they knew that The Lincoln was going to invade them shortly after taking office. Lincoln did exactly that and, to facilitate it, raised his own army of comparable size.
They didn't have to fire the first shot.
Not really. The Lincoln took care of that one for them when the Harriet Lane arrived in Charleston.
They could have done a lot of things, but they had their mind set on a fight from the beginning
History indicates otherwise. Davis left the senate by making a speech that pled for peaceful separation and against war. After the southern delegation left, the only remaining deep south senator, Wigfall, argued repeatedly for peaceful separation up until the day of the inauguration. He warned the yankees that if they sent armies and fleets and blockaders south, there would be a war. He warned them that war would bring devastation and massive loss of life to both. He even implored them to let the seceded states go and refocus their efforts on trying to convince the border states to remain in the union. But they did not listen - after all, they thought it would be a quick march south over a couple weeks and the whole thing would be settled. Lincoln thought this. Seward said it in even more explicit terms, telling others that things would be back to normal in a month or two. The yankees thought this all the way up to first Manassas. It would be a quick march to Richmond, they said. Well, all of that changed when the south, as Wigfall warned, resisted.
because they all knew that one Southerner could beat any 10 yanks.
I think the best was at Sabine Pass, where every southerner repulsed the equivalent of 13 yanks and half a warship. Needless to say, the predicted quick march to Richmond never happened. It took for long bloody years of invasion in which 100,000 more yankees died than did confederates.
Crampton's Gap has to come close where 2000 Union cavalrymen held of 26,000 troops under Longstreet for 6 hours. No warships, though.