When I used BlazingSEOllc, I was able to upgrade my plan at any time. It even discounted the price of the proxies based if I was in-between billing cycles.
You may want to contact support and tell them you want X amount of proxies, and how do do it. They were helpful to me when I asked.
I really dont see the need for rotating syntax. It takes to much time, and really has no difference in effect compared to using Dynamic Hashtags. As long as you have a big list of hashtags they will randomly rotate having the same effect as syntax.
I have over 300 hashtags for your niche, so that means that you can post 10 pictures every day, and every post will have unique hashtags.
You can add these 300 hashtags for as many accounts as you would like. If 10 accounts are posting pictures at the same time, their hashtags will all be different when using Dynamic Hashtags.