Your server - physically should have RAM for OS, all other applications/daemons you may be running on it, at least 2GB for Aerospike daemon plus whatever RAM you allocate in the Aerospike config file for each namespace. If you have one namespace, say has 4GB RAM specified (default), then that much RAM should be available in your server on top of the OS+daemons. Give yourself some headroom too. So, if nothing else is running on your server besides Aerospike, I would say you could run Aerospike with a 4GB RAM single namespace defined in the config file on a 8GB RAM machine.
Regarding the other part - about crashing - the only scenario that you must also tune is the namespace supervisor thread period. By default it runs every two minutes, round robin over all namespaces. That is the thread that detects HWM violations. grep for thr_nsup in /var/log/aerospike/aerospike.log and see total time it takes to run over each namespace and make sure your nsup period is higher than that. In that period, your data rate of updates to records should not exceed such that you blow past HWMs before nsup has a chance to run.