Hi
New to HE (24 Dec) not new to HA 
As I start migrating my HA across to HE are there any limitations I should be aware of?
I have about 80 Hue devices coming in through cocohue
16 ZWave TRVs, 10 off Zwave Thermostats.
and an assortment of 60 other zigbee/zwave devices.
Should I be considering a second HE and Mesh them?
I think you are plenty good with that count.. I have about 140 or so devices mixed Z-Wave/Zigbee. Some here have over 200 devices.
I do like using separate hubs though (either by location or by "type" i.e. Zigbee/Zw/Cloud). I think it helps distribute the load a bit and increase device range. However it's generally NOT required according to the folks at HE.
Another way to reduce load is by using an external controller like Node-RED.
On z-wave you have a limit of 232 per hub, and need repeaters for over 32 devices (any hard wired z-wave device is typically a repeater) Zigbee, your limit is 32 devices connected directly to the hub, and unlimited with repeaters (again powered zigbee devices are typically repeaters. Stay away from most zigbee bulbs as they make bad repeaters. If you need zigbee bulbs use a seperate hub. I recommend you use switches/dimmers for lights over bulbs)
@erktrek Thanks - looks like I will be OK for the moment, but will look at a second HE later.
@rlithgow1 Thanks - I should be Ok 95% of zigbee are hue lights on the Hue Hubs, the only exceptions are a odds and sods that won't run on the Hue Hubs.
I don't have any zigbee switches/dimmers and don't foresee the need.
99% of light actions are automated - try to keep users away from switches
Thank you both
Much appreciate your insights
Some newer smart switches can actually handle smart bulbs - they have a setting that disables physically turning the power off to the light fixture but still registers the event digitally.
Personally I prefer lutron switches/dimmers. They control all my lights. I have a couple of bulbs (sengled) for table lamps that can be turned off via pico switches. Then I have a pico on each night stand that the middle button turns off the entire house, makes sure that all the locks lock, and sets the led strip in the kitchen under the cabinets to .05.
I feel like you should be considering additional hubs but not necessarily purchasing one straight away. Based on @erktrek 's response, the total number of physical devices don't necessarily dictate performance, so best to take it slowly and keep the option of an additional hub in mind.
I have recently purchased a C-7 hub to compliment my C-4 hub, allowing me to move my 70-80 light/sensor Hue setup to the C-7 plus 1-2 dozen Zigbee contact sensors. This then allowed me to syphon off my less time-dependent Wi-fi smart plugs, thermostat and other Internet-based integrations to my C-4, allowing my direct device connections to be handled on the one hub. Not sure how much this may help your decision, but hopefully another user experience may help guide you through...
One thing to add to your last comment..... Prior to purchasing my C-7 I also had my lighting solely on the Hue hub, using All4Hue to achieve the fine-grained control I was after. Something I had been wanting and putting off was the ability to incorporate things like contact sensors and other devices into the lighting setup, given the complexity in getting status details back to the Hue hub. I haven't looked back, enjoying motion zones and contact sensors that keep rules "alive"... I do highly recommend it if you can afford to move your lighting onto a Hubitat hub.
I have 79 physical Zigbee/Z-wave devices on one hub, and 160 Hue/LAN and virtual devices on the other, this also has all my apps.
I do this as @erktrek does, I like to split them up and try to balance out what I need.
I've just bought a 3rd (a C7) I have no idea what I'm doing with this one as yet 
And also using Node Red here 
I don't think this applies to Z-Wave, only Zigbee (where it's implementation-specific, but 32 is indeed the number for Hubitat). Repeaters are still a good idea for both protocols, regardless of number of devices or distance from the hub; I just haven't seen this mentioned before and it's also not in the docs (which it is for Zigbee). Just being nitpicky and would appreciate correction if I'm wrong, but otherwise just thought I'd throw this out there (and did I mention that I'd use repeaters anyway?). 
I have been using 60 odd ZWave devices around the house without any issues or need for dedicated repeaters.
About half of my Zwave devices are battery operated the other half mains operated.
So I am able to see the mesh and the route etc device can take to get back to the controller.
I should be alright here
My biggest issue right now is trying to find a way to get HE to turn on the heating when a TRV / Thermostat shows demand for heat
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