How do denominations of christanity get satrted and how would one go about starting a new one

God's children shouldn't be separated into denominatons as it is. So instead of thinking to separate further, why don't you work toward bringing Christians together in unison as a mission in your Christian walk of life. Teaching God's Word doesn't need to be titled with denomination headers. Allow God to use you as a vessel for His Holy Spirit to work through and you can truthfully call it what it is... God's Word!

You start teaching one, get people to start to follow you, That is it,
Often they start when one group does not like what another is doing, for example issues like baptism or communion are issues between groups, or how you believe in things like foods or drinking.

The difference is how much you differ, to if you are a true new denomination or merely a independnet group with similar beliefs of a main denomination, and then your size,

For example our group has perhaps 4000 to 5000 members worldwide, we are just considered a church, not a denomination

Have you already viewed the listed denominations? And how each differ from each other?

God's Word mentions 7 churches in Revelations. I trust God has already veiwed, and distinguished the differences. In choice in my opinion is to follow that church which God found favor in. Revelation 3:7 the church of Philadelphia teaches Truth and holds the key of David. So does your church holds the knowledge of the key of David, and truth?

Revelation 3:7 And to the angel of the church in Philadelphia write; These things saith he that is holy, he that is true, he that hath the key of David, he that openeth, and no man shutteth; and shutteth, and no man openeth;

And Revelation 2:8-9 the church of Smyrna is rich in what it holds.

Perhaps it is better to hear what the other 5 churches do that God is against? Either way I would say the donominations should be christian, and holding to Truth of God's Word.