The C7 is stable and failsafe, but it's completely out of its leagues with 350 MBit/s wan speeds
(the hard limit is around 175-200 MBit/s).
Not with the OPs speed requirements in mind. Might still be nice to play around with, to get familiar with OpenWrt, maybe as addon wireless AP - but it's totally unsuitable to route 350 MBit/s.
The price of the rt3200 fluctuates quite drastically, with a little patience you may get it for 50-70 GBP though - and it's more than worth that much for a wifi6 wireless router.
Personally I'd lean towards the CR25ing as well, as it sorts out the routing speed problem quite reliably and should be a good match, combined with a decent AP, but with the OPs requriements in mind, the rt3200 might be an easier entry into OpenWrt. Do not count on the wireless option of the CR25Wing, only a single mini-PCIe slot and afaik 802.11n (ath9k), this needs to be outsourced to a proper concurrent dual-band 802.11ac/ ax AP.
The ASRock g10 is a nice device, much faster than the c7 and often available for rather little money, but 350 MBit/s is not far away from its maximum routing performance and recovery is not very user friendly (serial console required). For the right price still a great option, even if 'just' as AP.
BTW op I think you should stick to the 200 down from VM that's what I am on and go for the rt3200. I am onley looking at the x86 router because I have about 8 or 10 routers as back ups. lol I am running a r7800 as my mane router and a r6260 as a dumb AP. I picked the r7800 up off ebay for £20
Those 4-port x86_64 routers/ UTM appliances behave just like your classic router, in pretty much every way - just that they usually don't have integrated WLAN. luci is present as normal, the four ethernet ports aren't on a switch, but individually accessible and can be bridged, bonded or used for VLANs, sysupgrade works as usual - and they aren't less stable either (11:13:30 up 30 days, 8:12, load average: 0.00, 0.00, 0.00 - and the uptime is only that 'short', because I can't keep myself from doing sysupgrades).
two of them will work as a router (lan & wan, ignore markings on the chassi, openwrt does), the additional two openwrt doesn't really know what to do with, so they'll remain unconfigured until you decide to make use of them.