where are you from?
Certified FileMaker Hoster
fmphost.com is a good hoster - ask them, they provide answers quickly.
Seeing as you want to use server plugins etc, then if you have the budget, then you might want to consider having your own copy of FileMaker Server with as many concurrent connections you need for FileMaker Go, and use Amazon Web Services (EC2) Windows Server virtual server. There's a bit of setup involved but I've found it works very well.. I even set up a free tier t2.micro instance and it handled FMServer with WebDirect very well - speed was good. You can scale up the specs of the server instance to whatever you need and whatever your budget can afford...
I love macusa.net. They are always there for help and very quick about it. I've used them for years with many many databases. Concurrent connections is an issue with a shared server. Honestly I should probably have my own server but for me it's better to have someone handling the server stuff, gives me more time to concentrate on other work.
As for you special requests, I can answer that but I know they folks will work with you.
I'd love to see a blog post on how to go about this, I've never had the time to really get to grips with EC2, be great to see some examples...
Hey Hank!, long time no see! , good to see you back.
I've been working for years with a Texan company called Kickass VPS.
They provide fast virtual servers at an affordable price with one to one customer service. I'm very happy with them.
Their main datacenter is located in Dallas but they have also the west and east coast covered so I recommend them.
P.S.: Every time I tell to a customer "May be I'm wrong, but I'm not..." I remember you . Glad to see you back.