There are all sorts of potential issues that you will need to deal with over the next 12 to 18 months. Sorry this may well come across as a bit negative but you need to be aware so that you can deal with them effectively.
I agree with the poster who said you have been let down by the previous chair and vice chair. They should have had some proper process in place for continuity. My concern is that you say that they will still be on the GB and will be a great help. I think they could be a hindrance and be busy leading from the back seat. I think you need to accept that you may need to stamp your authority on being the Chair, if they interfere too much.
Your best two allies are potentially the new head teacher and the person who carried out your governance review. You need to get to having a productive relationship with the new head teacher as soon as possible. They will probably want to have a period of time in school assessing the situation before they start to do anything different. I would look to set up a time span for this with their agreement so you both know that there will be a period of apparent inactivity whilst they get to grips with the politics etc in side the school. As chair i meet my head teacher every 2 weeks for 60 minutes. We do not make any decisions it is an opportunity to let the head teacher say how things are going, say anything they want to say about issues in the school and generally allow you to build a relationship between the two of you. I cannot emphasise too much how important the relationship is between head and chair.
I would expect to loose at least a couple of staff over the first 12 months of a new head teacher as they introduce new ways of working. The fact that you are RI says that the loss will be greater if teaching is not that great.
Also be prepared for the new head saying that things are far worse that has been suggested by the RI ofsted report, that frequently happens when a new head comes in and sees the detail. How good is your standards in the school and do the Gb really know what the standards are where they are going to.
I hope that the governance review was carried out by someone who is a National Leader of Governance (NLG) and knows what they were doing. You need to talk with them at length about what they found and more importantly what they think needs to happen to improve the GB and the school. There probably will also be somebody who is helping the new head so they are also somebody that you need to get to know and tap up to see what they think is wrong in the school.
I am going to guess that you Governing Body has just been going through the motions in terms of trying to improve the school's situation. You probably need to consider how you will operate meetings in future. They need to become positive but also challenging to the head teacher and you need as a GB to be asking questions. That brings up the subject of clerking. Who is doing the clerking? Can you on the minutes of all meetings see impact, see questions and answers being given with clear decisions and actions being taken. If not then you are not running the meeting right and probably you have the wrong clerk in place.
I would invest in membership of NGA, as it keeps you and the Gb up todate on what is happening. Personally, as a chair of governors, I do not like the Key but I know many head teachers find it very useful, so they may want to invest in it. I would be asking as a new chair for an NLG to act as your mentor and adviser, that should be free and is another person on the end of a telephone line for advice. As an NLG I have regular contact with about 6 chairs of governors who are at different stages in terms of their experience.
Bottom line, go for it and be bold. You will have some bumpy times but the feeling of having achieved something, especially when you get a good ofsted report, is worth it. You need to concentrate on school improvement not going looking to become an academy, so that should be 12 months plus down the line, unless somebody from the regional schools commissioner comes calling in which case you will not have any choice in the matter.
If you want to talk privately please PM me