I'd suggest getting started with just getting two (or more) Heltec v3 devices, flashing them with the Meshtastic firmware and tinkering around.

https://meshtastic.org/docs/hardware/devices/heltec-automation/lora32/

Links to buy are at the bottom of that page. Just a warning: the stock case doesn't have room for a battery. But it can be powered via USB-C, which works fine if you're just tinkering around. If you want to go mobile, you'll need a cellphone battery pack and a USB-C cable. You can get a 3.3V battety (any LiPo will be fine), but you'd have to use double-sided tape or something to keep it from flopping around and breaking off.

If you want to get into piecing together your own hardware from parts, trade offs between different components, and all that, check out the vloggers. There are many YouTubers yakking about this, and I hate to say it, but they're a pretty good source of information despite frequently being paid by the people that make the gear they're recommending. Just make sure to hit a variety of them who are shilling different gear to try to understand what their biases are.

In the end, going the more advanced route is likely to be expensive and time consuming. I'm speaking from experience. I've now placed 3 orders from RAK Wireless and I still don't have enough parts to make a single node. I think I will once this 3rd order comes in, but it's been frustrating and a bunch of money wasted on shipping costs.

Full disclosure: I do not get any money from anyone for helping people get started with mesh networks. I just recommend the gear that's worked for me.