Upgrade single user site to multiple user site and check PHP code etc.

I have a website with a compliance system on. It’s developed for one company to use. I want to convert it to multiple company use. Here are the tasks as I see it (there might be more): • Firstly, I need you to go through the code, check it, test it so I am sure that it’s working perfectly and it’s optimized – No reason to let more companies use it if it has some bugs. Fix any issues first. So you have to check the features and functions of the site, become familiar with it, get to know it like you made it. Test it, make sure it works perfectly. Also please check if the DB is optimal. • Suggest improvements to the system, now that you know it so well. Are there any ways we can make it better, more stable, faster or ? • The system today has 2 escalation levels, please let me know how much it would cost to allow the user to only have 1 escalation level. This should be something each company would choose. I guess we could either do it where the escalation levels are not “required”, but still showing or we could make it so if the company select only 1 escalation level, they can only see 1 and the other is hidden. Please let me know the price difference and what you recommend as the best solution. • Add feature so multiple companies can register and use their own version of the software completely isolated from other users. The cases, docs and users they add cannot be seen by other companies using the system. • Add backend admin where I can see all the different companies and their users who signed up and am using the system. I should be able to edit their data, delete them, and add new, see if they are on free trial, any payment info etc. Backend should be made in the AdminLTE admin template. • Also let me know if you think it would be better to convert the current site/code to a newer framework, or better. Can we make it more smooth, work better for the user, more stable? This is not a necessity, just checking if it would be an advantage to do it, since we are already upgrading. Let me know your recommendation and price. • Finally, I want to implement a 14 days free trial and after the 14 days, it will cost $9.99 per month to use the system. I will apply for a payment gateway with 2checkout and also use PayPal. I will need those implemented as well. Please let me know a timeframe and your budget for this.