any suggestions on light bulbs, sensors and switches suitable for use with c7 i have been using meross and aqara mainly with echo
Welcome. There's a list of compatible devices in the Hubitat Docs. That's a great place to start.
There are also lots of discussions about various choices here in the community forum. A search will get you more information than you want probably.
By the way, there's a link to that doc right at the top of your devices list. I missed that for about two years... It's handy.
It's a difficult one to answer...It depends on whether you want to use Z Wave, Zigbee or some other integration (Philips Hue etc). Many prefer Zigbee due to it being a little snappier, cost and availability of devices, easier to manage. I've always used Z Wave devices as my first devices were Z Wave and I wanted to build a single strong mesh. Also due to congestion in the 2.4GHz spectrum I'd rather stay away from anything that uses similar frequency to WiFi.
I use Fibaro Dimmer 2 modules for my lighting. These are fitted behind switches that I've converted to momentary/retractive switches. This allows me to have the lights in automations, but importantly, retain full manual control. As the modules sit between the switch and the load, even if the hub was removed I'd by able to turn on, off and dim the lights from the switch. In the UK Z Wave dimmers are available by Vesternet, Fibaro, Aeotec and Qubino. There are also options for Zigbee and they're likely to be cheaper from the likes of amazon, aliexpress (Sonoff etc).
I don't use a lot of sensors - I have a few Fibaro Motion sensors and the odd contact. I've got my alarm system sending mqtt messages though a Raspberry Pi so that all of the PIR's and door contacts etc are mirrored in Hubitat. It's cheaper and easier for me to add a device to my intruder alarm and program it than add another battery powered Z device direct to Hubitat. As you're in the UK that would be a possible route for you too. It involves replacing your alarm control with Honeywell Dimension and adding a VMOD, which is a communication module. That comms mod reports the status of the zones on the alarm via mqtt and will also provide full remote control of the alarm system via the app. Information is at www.selfmon.uk