2 Cor 9:6-8
6 Now this I say, he who sows sparingly shall also reap sparingly; and he who sows bountifully shall also reap bountifully. 7 Let each one do just as he has purposed in his heart; not grudgingly or under compulsion; for God loves a cheerful giver. NAS
When the Biblical tithe is totaled it come to about 33 1/3% not 10%. The various tithes were for various purposes, the one mentioned in Mal 3:10 is to feed the poor not support a church.
The concept of a 10% tithe predates the law.
Gen 14:17-20
17 Then after his return from the defeat of Chedorlaomer and the kings who were with him, the king of Sodom went out to meet him at the valley of Shaveh (that is, the King's Valley). 18 And Melchizedek king of Salem brought out bread and wine; now he was a priest of God Most High. 19 And he blessed him and said,
"Blessed be Abram of God Most High,
Possessor of heaven and earth;
20 And blessed be God Most High,
Who has delivered your enemies into your hand."
And he gave him a tenth of all.
Gen 28:22
22 And this stone, which I have set up as a pillar, will be God's house; and of all that Thou dost give me I will surely give a tenth to Thee."
I see giving to the work of the Lord as a sign of trusting Him to fulfill all our needs more than a legalistic command to support any particular church.
As to baptizm I see this as an act of obedience to our Lord and a public statement of our faith in Him as Lord and Savior. We should be baptized as soon as possible after salvation. Age is immaterial, commitment and faith should be the determining factors.