The container itself has been allocated 4 cores and 4 GiB RAM on my PVE host, RAM usage currently sits at 75%. Before I had 2 GiB of RAM allocated, felt like it was slowed down a little bit by running from a HDD then. The host CPU is an i5-9400, so nothing beefy.
Besides Gitlab, I run Home Assistant, a single tenant Nextcloud instance and pfsense on the same host without any troubles. All services combined have 14 GiB Ram allocated, most of that actually goes to HASS since its doing speech recognition and speech synthesis (6GiB)
Also: unbuild the thing