Benefits of staying?
Free trade
Both the EU and UK want a free trade deal. It's in both our interest for this to happen and is central to the future relationship statement that is already on the table in may's deal.
No Irish border issue/tensions in NI
Simple solution, and I hope it still happens, is that NI stay in the single market. Solves all issues and would be great for their economy as many firms would undoubtedly open offices there. This would undoubtedly already have happened if we hadn't allowed ourselves to be dictated to by a handful of DUP MPs
Control of our borders for non EU citizens
Not sure what you mean. There would arguably be less control of our borders for none EU citizens as we would be issuing work permits to those applicants most suitable to the jobs on offer, rather than based on where they come from.
Workers rights
Why would this change?. Same with citizens rights. There would be a bill to adopt all EU laws and May has already said this wouldn't be affected. Even if they tried to change in the future it would have to be passed by parliamentary bill, which can always be reversed at a later date.
Free movement within the EU
I'm not going there again with my views on this. but they are well documented and NOT racist if you care to look back in here a few weeks. As regards existing EU citizens in the UK and vice versa, perfectly reasonable arrangements are in place to ensure indefinite right to remain should May's deal be implemented.
UK manufacturing base an access route to the EU market
A free trade deal would cover a lot of the issues with this. Otherwise the manufacturers just need to make sure they keep up with any EU changes. Initially, all rules are met as we are currently part of it.
Access to the European Court(s)
Not sure what point you are making
Secure and working supply chain.
I don't understand why this would be any problem. We have a need for jobs that we can't fill from those currently in the UK then we advertise abroad and issue work permits
Security for London (and Edinburgh) as leaders in the financial markets.
If we have a free trade deal I can't see what the issue would be. The concern at the moment surrounds a no deal and all the uncertainty.
Thats without going into detail re numerous pan EU cooperation arrangements that others such as
@Bruce Wayne are more familier with.
Again what's the problem. We just pay to be members of that particular arrangement, and the other E27 would be happy with this as generally we also bring a lot of expertise to the table.
All the main concerns relate to a no deal which I think we can be fairly certain now will not happen. We will either stay in the EU or leave on a negotiated deal which will not hurt the economy anywhere near as much as a no deal.