Ad. 1. Nope, briefly said:
- EXOS - flagship switching/routing solution (could be called L3 switches), works for campus, datacenter, core, pure L2 or L3 networks... but all depends on features and applications you need. If you take a look at the EXOS User Guide or Feature License Requirements or EXOS Datasheet (https://kapost-files-prod.s3.amazonaws.com/kapost/55ba7c9e07003d9aab000394/studio/content/57dbfb2f330db0dec00000b4/published/extremexos-r-data-sheet.pdf) you will see how much is there. For L3 you have all you might need in many scenarios (OSPF, static routing, BGP, PIM, VRRP etc.). However, there is no NAT so far, and buffers are rather small (so less room for rate shaping) compared to SLX switches and routers that can have up to 6 GB buffers! If you were a reseller, you would have to think what are the customer requirements and based on that propose him topology and boxes. From Extreme's strategy, EXOS is dedicated mostly for campus deployments (traditional 2-3-4-tier hierarchical designs, rings...), yet having EVB/VEPA/DirectAttach feature that prevents vSwitches from switching, so there is full inter-VM communication seen and controllable by the physical switch. Besides... heterogenous stacking, telemetry, Policy, Python scripting/processes, three types of APIs, CLEARFlow, virtual routers and VRFs...
- VSP - ex-Avaya awesomeness, Extreme now posesses the best implementation (as from the very roots) of IEEE 802.3aq Shortest Path Bridging (and extensions that hopefully will become a part of the standard in the future) fabrics that is a pure gamechanger. I'd love if you guys who are more Cisco-fluent could comment on L3-everywhere approach (with hassle of spanning the broadcasting domains, multicast routing and failover times for critical network-wide services) and compare it to L2-everywhere approach that is doable with SPB. Spanning Tree is not a challenge today (many networks should not even need STP for typical hierarchical network - just LACP and ELRP). Besides, it also supports traditional L3 features, but I'd use them rather for interoperation with non-SPB parts of the network. VSPs are also meant for the campus deployments but suit in the DCs as well, they have nice feature useful there called DVR;
- ERS - ex-Avaya switches meant for access, but still, I see OSPF, PIM, just no BGP. ERS and VSPs mainly have MACsec where EXOS just started with an adapter and X465 which supports MACsec on all ports natively;
- VDX - ex-Brocade switches dedicated to data centers; really nice, with TRILL-based approach to fabric networks, some pros and cons compared to SPB but don't treat those two as an ultimate solutions for every customer possible. They also got flexible configuration ports (Ethernet/Fibre Channel) and IP-fabric for L3 leaf-spine fabric networks;
- SLX - ex-Brocade switches and routers dedicated to data centers, with extremely high level of automation (EXOS and VSPs are going to that point pretty nice over time), huge buffers, auxilliary applications that came along during the acquisition, and KVM environment to install VMs for no-delay-impacted analytics. SLX 9850 is of 230Tbps capacity BTW, that's a big boy. If I found just a chassis of that one, I could pay most of my mortgage
- All the above can fit in many scenarios, and for example EXOS was and still can be successful at service provider and transport networks, SLX is also not meant only for some DC-room and so on... Just to harness the amount of nice technology Extreme has they decided to specify some use-cases and verticals that the solutions are best suited for; what is nice, they do implement functionalities between platforms. That's why X465 now has also KVM environment like SLX does;
- There are also some CER/CES/MLX boxes but never saw any campaign with these.
If you want to be well-suited for your job it would be good if you knew what platform do they use. EXOS and SLX are two different worlds when it comes to CLI (BTW SLX and VDX is very similar to Cisco). But if you started the topic with mentioning EXOS I believe you should not worry about SLX right now.
ECNA - EXOS Fundamentals and ECS - Campus EXOS Switching & Routing are pure EXOS classes. There is also separate ECS class for SLX.
Eh... sorry for a bit long post. Not long enough to fully and precisely elaborate on the topic but... Yeah, EXOS can act as a router.
Hope that helps,
Tomasz