Please forgive my naivete.
I am looking to replace a Ubiquiti network setup consisting of:

• USG Pro X8 Firewall/Router
• Unifi 24-port managed gigabit switch
• 4x Unifi AP-AC Pro wireless access points
• Unifi Gen 1 Cloud Key

From what I have read, I can replace the firewall and switch with a Mikrotik CRS328-24P-4S+RM running RouterOS and the 4 access points with 2x cAP ac + 2x wAP ac devices (two indoors and two outdoors).

Is this correct? Also, can I manage these remotely? Can I set up a captive portal for wireless guests? I only have Linux machines to work with. If this works out for me, I plan on implementing a reduced version in a vacation home I am building.

Maybe yes Maybe No.
All device with RouterOS have complete software features, but the switch (like CRS328-24P-4S+RM) are "slower" for firewall/router/captive portal use...
Look at the performance in datasheet for an idea of the speed. If it isn't enough for the speed of your internet connection, add a router at your schema.
Take a look almost on an HAP AC2 (if you have an FTTC) or RB4011 (if you need more speed for an FTTH).

Agree with previous post...

I use a 2011 for 500/50. The ac2 should be good for 1000/100, but it has only 16MB flash.

CRS with 600MHz MIPS CPU should route like the 2011. With dual-core 800MHz ARM CPU it should be passable for 1000/100.

The single-core 800 MHz ARM is only a bit faster than the 600 MHz MIPS.

But the 650MHz MIPS is showing as slower than the 600MHz MIPS.

Note that many CRS also only have 16MB flash.

The 4011 does not cut it if you want a host to run faster than 1 Gbps.

@vortex Why is 16MB of flash a concern? If you need extra storage for logging or whatever there is USB on the hAP ac².

Ultimately my internet connection is going to be symmetric gigabit.

A creative solution is (if your WAN connection is coming in the correct place) to use your setup but use one of the CAP AC's as router, as this has a much faster CPU than the CRS (and has two ethernet-ports..)
Best bet is still a separate RB4011 or something to to the routing.

@vortex Why is 16MB of flash a concern? If you need extra storage for logging or whatever there is USB on the hAP ac².

Search for '16MB' and you will see that it still seems painful.

I have few notes about RB4011:
mounting ears are terrible if you plan to install this router to rack.
Switch chip is not the best inside of RB4011.
Despite all of that RB4011 has good HW characteristics.
Also you can use CCR1009 if budget allows that and no switch chip is needed.

And with regards to the wireless part:

- cAP ac and wAP ac are the obvious alternatives (the cAP ac has 2 x 2 where wAP ac and AC-Pro have 3x3)
- though injectors are supplied, I would use a POE capable switch
- CAPsMAN is great! Tuning is some work (learning curve is comparable with Unifi)

Remote management can be achieved, you can use SSH of WebFig (preferably through a VPN tunnel).

I am unaware of ubiquiti routing but you will not get arguments about the superior performance of ubiquiti wifi from many here - but at a cost differential.
I can understand moving to MT routing and perhaps some of their newer switches but not necessarily to the wifi side of the house.
Points to the question, why the desired change???

Why the desired change???

I had been listening to certain podcasts on this topic and the host had glowing reviews for Mikrotik equipment and a lot of disdain for the dubious management practices at Ubiquiti. Granted, he did admit that there is nothing wrong with Unifi gear itself, just Ubiquiti's methods for gathering data about its user base.

With that in mind, I was trying to see what it would cost to switch and what the operational differences would be. Looks like I will be sticking Unifi for now.

With that in mind, I was trying to see what it would cost to switch and what the operational differences would be. Looks like I will be sticking Unifi for now.

MikroTik doesn't really have anything to compete directly against the AC Pro (I guess), the cAP AC is close but not really apples to apples.