I have read you requirements and to be fair they are impossible to meet, anyone who states they can achieve them is either experienced or not being completely honest with you or themselves. Why you ask?
1. Setting milestones with delivery dates can only be achieved accurately when only one party is involved, when going through the process of acceptance and changes with the client these dates can move right quite quickly.
2. Your budget is quite low considering you require all rights to everything including IPR, especially when you are requesting high expertise surely you realise expertise comes at a price as does IPR.
3. Certain SEO requires specific content laid out in a certain way, yet you wish to edit and amend content at will, whilst expecting your freelancer to provide a highly optimised SEO site.
4. Performance of the site can only be as good as the framework it is using, this means the freelancer would only ever achieve the performance of the framework and no more.
5. You have laid out 5 milestones along with percentage payments, four of those are at 20% which equates to 80% and one at 25% that is 105% which is in it self impossible.
Question 1, I have far too many to list here and not just in wordpress covering more than just ecommerce.
Question 2, I am very experienced in many frameworks wordpress is just one.
Qusetion 3, This could only ever be a guide due to the involvement of the client as explained earlier.
Are you sure wordpress is what you need?