So I think I've made some mistakes during the writing of this post and also mistakes trying not to openly comment on my subnetting.
The ip address used on the ve interfaces is wrong. It's a typo. The correctly IP addresses for the ve interfaces end in a .1 indeed and no .0 (sorry bout that).
My router's ip is not 192.168.1.1 actually, it is 10.0.0.1/24
To clear up things (sorry bout that again) this is my current setup on the larger switch (layer 3):
it has 2 vlans: 30 (users) and 200 (voice). All routing is done on this switch and it has a static route to the router (ip route 0.0.0.0/0 10.0.0.1). Actually I would like to only hit the router for external (internet) requests.
Now what I would like to do is to integrate an extra switch (12 port) into this. I know I can stack them but as a learning escenario I would like not to as this would be my common case.
As a way to separate users (not voice) I would like to place them on a different subnet (10.0.4.0/24) on the smaller switch.
Do I need to turn the smaller switch to a layer 2 for this or can I keep it as layer 3?
The new vlan 40 (10.0.4.0/24) should be declared on the big switch, small switch or both?
I would like both switches to communicate through a lag just so I can have a backup connection in case the first one goes down.
With the implementation of both switches I would still like to keep the routing inside the switches and only hit the router for internet access.
BTW, large switch has a static ip of 10.0.0.11 and that how it communicates with the router back and forth.
Next step would be to learn about spanning tree and then about voice priority.
Honestly, it sounds like this is a small network and probably doesn't need routing configured.
Having two devices with vlan 30 configured, but with different IP addressing will require routing, and you'll need to keep the traffic separated by a routing device (could be static routes).
Unless you have a reason to have a separate broadcast domain/routing environment (say this were at a remote site rather than in the same IDF/building), I'd probably keep all of your users on the 10.0.0.0/24 segment instead of introducing 10.0.4.0/24...
The 10.0.0.11 ip address on your larger switch is very likely only used for management purposes, not for routing.
What was said above about stacking being an easy solution for extending the configuration to another switch for ease of management is 100% correct.
If you're not stacking the switches, you need to identify how the traffic is passing back and forth between the switches and while untagged 30 and tagged 200 will work, it would be cleaner to have tagged 30 and tagged 200 for the "trunk" port.
You didn't mention brand of voip phones - chances are very good that configuring LLDP-MED will help with the voice vlan assignment for your phones.