Yes, you can expand your network with two CRS305s and a fibre link in between. The CRS305 offers four SFP+ ports suitable for 10 Gbps connections and a Gigabit Ethernet port for management purposes. By using fibre links, you can connect the switches over longer distances and thus expand your network.

You can find more information about the facts of the case at https://wiki.mikrotik.com/wiki/S%2BRJ10_general_guidance. The problem with overheating occurs with almost all passively cooled solutions on the market. Unfortunately, not everything about Mikrotik is always described conclusively on the product page. The target group is clearly the professional low-budget market. Therefore, it is often assumed that the customer knows his way around. This is not always to the benefit of the brand. The fun starts with the fact that with SFP+ solutions it always depends very much on what kind of modules are used. Old 10 Gbit/s copper modules of the first generation had up to 12W of waste heat. It is almost impossible to dissipate this passively. The waste heat arises because with 10 Gbit/s the switching times are very high and therefore the switching losses of the control electronics increase immeasurably. The longer and worse the cable, the more unpredictable (large capacities, resistances and inductances). According to the manufacturer, the Mikrotik S+RJ10 modules require 2.7W for 30m of cable. The specification of the mentioned switch specifies a maximum of 8W for the 4 modules. Equipped with 4 copper modules, one would therefore theoretically already exceed the limit. Please do not connect 100m of cable per module. At the end of the page linked above, it is also clearly stated that you have to provide additional cooling for passive switches if you do not leave out a slot between the modules. Experience shows that it is usually possible to place an optical module in between, which normally only requires 0.4 to 0.8W for up to 300m. As Thomas has already written correctly, in this case either active cooling is necessary OR you switch to optical modules (fibre optic multimode) OR you use passive or active DACs (Direct Attached Cable). The last option is by far the cheapest, if you can design the cabling accordingly. Multimode module: https://mikrotik.com/product/Splus85DLC03D Passive DAC: https://mikrotik.com/product/xs_da0001 (1m) Active DAC: https://mikrotik.com/product/s_ao0005 (5m) Once you get the hang of Mikrotik, you really get a lot for your money. It may take a little while until it's ready ;-)

Nur 2 Ethernet Module sind unterstützt in CRS305. DAC Module für den Server und Switch sind besser. https://wiki.mikrotik.com/wiki/MikroTik_SFP_module_compatibility_table

Here are a few "learnings" from my setup: 1. consider using the CRS309 for one side. It seems like a lot of devices, so maybe you can save another switch (less cable clutter/socket power consumption). then you have 8+1 ports. 100/1000MBase-T SFP+ are quite cheap at fs.com (see next point). 2. fs.com has a much better and clearer selection of transceivers and cables, and some of them are significantly cheaper. 3. in my experience optical transceivers from different manufacturers work well together. I have taken multimode, Ubiquiti UF-MM-10G: Set of 2, but they also link to generic compatible 10GBASE-SR SFP+ 850nm from fs. But there are certainly people who absolutely recommend singlemode. Honestly, I don't think it makes much difference to your setup, you don't want to wire up a whole house and swapping is quick (if the cable laying isn't too tedious). 4. do you really want to do a LAG on 2 10G connections? srsly? Do you really need that much throughput, really? Because of: 5. 10G transceivers and also the switch get HOT! around 60°C (ok, specification is up to 75, but the next hot summer is coming for sure...) and it doesn't seem to matter if it's fibre or copper, for me the optical modules show a higher temp than the 10GBase-T ones. And that would be another reason for point 1: the CRS309 at least has a cooling grate and more space to distribute the heat. Hope that helps

The RJ45/PoE port is 1Gb. The 4 SFP+ ports are all 10Gb capable, provided the correct DAC cables or SFP modules are used. The PoE port can be used as an uplink to the existing network. I don't know exactly what you mean by input. Any switch port can be used as an uplink/downlink.

Hello :-) No. When you buy this product, you do not get a 19'' rack kit. There are also no holes provided to attach the kit. I would recommend a 19'' rack shelf to put on top ;-) Greetings

Yes you can, unfortunately I didn't find anything suitable for copper at Galaxus, then I found what I was looking for on fs.com: Generic Compatible 10GBASE-T SFP+ Copper RJ-45 30m Transceiver Module, https://www.fs.com/de-en/products/74680.html, running continuously since August 2019 without problems :D