So,what is your definition of "Separation of church and state"
God alone is Lord of the conscience, and He has left it free from the doctrines and commandments of men which are contrary to His Word or not contained in it. Church and state should be separate. The state owes to every church protection and full freedom in the pursuit of its spiritual ends. In providing for such freedom no ecclesiastical group or denomination should be favored by the state more than others. Civil government being ordained of God, it is the duty of Christians to render loyal obedience thereto in all things not contrary to the revealed will of God. The church should not resort to the civil power to carry on its work. The gospel of Christ contemplates spiritual means alone for the pursuit of its ends. The state has no right to impose penalties for religious opinions of any kind. The state has no right to impose taxes for the support of any form of religion. A free church in a free state is the Christian ideal, and this implies the right of free and unhindered access to God on the part of all persons, and the right to form and propagate opinions in the sphere of religion without interference by the civil power.
Does that mean that Christians should not vote
No. If Christians have the opportunity to vote, they should use the opportunity to exercise that opportunity in a spirit of Christian love for the flourishing of others. A Christian must place Christian values over political party, country, or tribal affiliations.
Does that mean that Christians should not run for office
No, but a Christian must not — in a general sense — try to use the power of compulsion (the sword of the government) to impose religious practices or convictions upon others.
Does that mean that pastors should not run for office
No, but pastors should understand that they must serve all people, not just people they like or agree with.
Does that mean that a pastor should not preach any message about a political issue
The gospel has political consequences, especially for social and economic justice (read the OT prophets), so biblical teaching along those lines is essential. However, shifting from biblical principles to endorsements of candidates undermines the ministry of the church and makes it a political rally instead of an outpost of the Kingdom of God.
a) would that include policies such as abortion and hom0se/ual
b) are there other political issues that are ok
If the Bible has something to say about a social issue, the pastor should preach/teach what he or she believes those passages mean.
Should a church invite a politician to speak in his church
I won’t definitely say no, but I can’t think of a good reason why a church should have a representative of one of the kingdoms of this world speak to a congregation during the scheduled time of worship.
If a politician wants to speak to the church community, make arrangements to do it in an area not devoted to worship and preaching; separate from normal worship times.