1 -- One is for God, of course; however, 1 is not a number w/ a lot of Biblical significance.
2 -- Two is the number of Humanity (we are male + female). This number does show up some in Biblical symbolic usage.
3 -- Three is innate perfection. Think of the stability of a 3-legged stool: it is in balance. The Trinity is the hidden, perfect nature of God. Threes shows up a lot in Revelation, esp. as additions, multipliers, and fractions. The 3 Woes are the ultimate agony of the judged creation. When the Horsemen destroy 1/3 of this or that, they are wrecking the world past the point of repair. The Number of the Beast is Six Tripled (666, see below).
4 -- Four is the number of the created universe (4 compass points, 4 winds, 4 corners, 4 "living creatures" surrounding the Throne). Four is used a lot in Revelation. The 4 Horsemen demonstrate God's judgment on the whole earth. The blood of the God's winepress flows for 1,600 stadia (4 x 4 x 100 = the entire creation, meaning everywhere).
5 -- Five is not a number of Biblical significance, but was used by medieval mystics as the number of Christ (for his five wounds). The 5-pointed star, or pentagram, is thus a Xtn symbol (and the heraldic device of Galahad).
6 -- Six is the number of Sin. Sin is "falling short," hamartia in Grk. 6 is short of 7 (see below), therefore the number of incompletion, of failing to achieve what one should. There were SIX stone jars for the Jewish rites of purification at Cana (a subtle dig at the incompletion of the Law). The Mark of the Beast is 666, or Six Tripled = the Essence of Sin. The dragon has six heads wearing diadems (claiming divine royalty).
7 -- Seven is the number of Completion, Fulness, Perfection. The 7 Thunders are thus the Voice of God himself; the 7 Stars are all the angels of all the churches; the 7 lampstands are all the churches throughout the earth; the 7 seals on the scroll of God's judgment indicate it is the Last, Ultimate Word on the fate of the universe; the 7 bowls of God's wrath are the entirety of his punishment of sin. 7 years stands for the entirety of human history, divided into before and after by Xt's coming: this is why 3 1/2 years = 42 months = 1,260 days is such a big deal.
8 -- Eight is not a biggie in Biblical symbology.
9 -- Nine shows up some in the Bible, more in later Xtn writings, as another number for perfection (3 x 3).
10 -- Tens, Hundreds, and Thousands are used to intensify things. A myriad -- 10,000 -- was the largest named number in the ancient world. "The Lord is coming with his holy myriads." 1,000 years is thus any significant stretch of time. The 1,600 stadia referenced above is 4 x 4 x 100 = everywhere. The 144,000 who will be saved is 12 x 12 x 1,000 (see below). Horns (animal horns, but also architectural projections -- something phallic here) signify power, esp. political/military power; 10 horns on the Beast is thus an indefinite, but large amount of clout -- perhaps a faction or train of vassals.
12 -- Twelve is the number of the People of God. There were 12 tribes of Israel and twelve apostles. There are 24 elders (12 + 12), meaning both the OT and NT church are included in the whole number saved. The 144,000 referred to in Revelation (12 x 12 x 1,000) thus means "everybody who is to be included" -- it's not a limiting number, but an expansive number. The City of God is measured in Rev. 21 as being 144 cubits square by man's or angel's measurement, meaning that it comprises all the People of God (12 x 12) and that they are coextensive (square, 4-sided) with the New Creation, and we know we are talking about people, not structures, because we are using a measure gauged to the capacity of men and angels (all souls).