BGP hub

I’m planing to use MK RouterOS x86 server platform like a BGP hub e.g this machine will terminate more than 500 BGP sessions with other MK routerboards. My question is : are there have any software limits for this? What kind of hardware I need to buy for fluent working setup.

In other way… I don’t strongly need a BGP routing in this project, just want to guarantee a non-interruption of traffic flow from clients to central spoke. The main scheme is

client1 — IPinIP tunnel – Central Spoke
| |
| ----IPinIP backup tunnel --|
I’m looking for something like cisco ip sla monitor still can’t find anything useful. Any suggestions ?