I picked up a MikroTik RB5009UG+S+IN myself but until now it really has not been a walk in the park, trying to get OpenWrt onto it. The SoC inside it is well supported though (Marvell ARM) so once the kinks get ironed out it should get better/easier. But getting OpenWrt on the Ubiquitis is a piece of cake, compared to it.
The memleak might get solved, but I am not skilled enough to look into it and the people who are can't narrow it down at the moment. The hardware support upstream (in the Linux kernel) is not what you'd want it to be for a device you'd expect to use for a few years. To illustrate: some of the Octeon code got removed for 5.9 I believe, only to be added back a bit later. That's telling. That's not something kernel maintainers do on a whim.
The hardware recommendations subforum is a good thread to start, and this post might get you on your way a bit: