Hello There!
I've read your requirements. It seems you are looking for someone who can help you out with changes in an already working c# application
I've worked on various projects that have complex architecture. I’m very well versed with standard practices for creating websites in ASP.Net MVC, Web Forms, Ajax, Angular.
Please share more details and we can further discuss.
P.S. – The proposed cost is an estimate. I could give you an exact figure, time-frame and what I expect to be able to accomplish if we talk. If any of the above sounds interesting, reply to this and we can discuss further.