Running full tables with ER Pro should not be a problem. Example of memory usage: https://community.ubnt.com/t5/EdgeMAX/Full-Tables-on-Edge-Router-Pro/m-p/787774/highlight/true#M27922
A single router is lot easier to configure, but introduces a single point of failure, of course. On the other hand, the complexity of dealing with VRRP and OSPF for two routers creates additional opportunity for failure, so if networking is not your forté I would not go there.