I'm not affiliated with these guys or anything. But the "bang for the buck" with them is really crazy. You can't beat the value here.
If you need a server in EU you should really check them out:
http://www.ovh.co.uk/
For under 80€/month you can get a full dedicated with a full pipe of 1GBPS bandwith, SSD disks and 16-32GB of memory. And you can get IP blocks there for $1 per IP/month.
OVH has a decent network and facility! We've used them for special customer projects. Their support is absolutely terrible but once your hardware is up its a pretty good place.
Source external consulting for your software side.
Keep in mind that ideally you want the server(s) to be near where your target users are, not where you are, to minimise latency for faster page loads.
You can get away hosting almost anywhere, you want to use a geographically distributed CDN for all your landers an graphics.
Depends on how you have it set up, I guess. If your landing page is static, and you're just firing tracking pixels that are hosted on your server, then the landing page can be on a CDN and your pixel latency is probably not going to matter much.
If you need to dynamically generate your landing page based on parameters then you can't CDN that (and CDN'ed images will be delayed), so the initial request latency will matter. For the final redirect, or if you're just direct-linking, the latency of your own server is probably going to be dwarfed by the terrible redirect times of most affiliate network servers anyway (or worse, for multiply daisy-chained brokered offers).
Then again, all the standard tracking/redirect platforms are so poorly designed that they'll probably dwarf the geo latency difference as well.
I just checked them out and they also have a datacenter right on the east coast on NA. They also let you try their servers for free for 1month if you're a UK registered business!! Just ordered mine, I'll let you know how I get on.....