The challenge of connecting the network of two building

Scenario

I am working in a company where the building with 3 floors (ground + 2 floors) and the current network is running normal is mixed CAT 5 and 5E, 3Com 4200 series / HP 1910 series manager switches 10/100/1000 Mbps twisted pair with about 160 devices (130 employees workstations and 30 servers, equipment) with available space for another 50 employees workstations, complete 210 max (average of 70 per floor).

Beside this building, wall to wall, a new buildingis being constructed, the same level of height 3 floors and with a maximum capacity of 300 (100 per floor). Unfortunately, the budget is low, I'm alone with only with the help of an intern and electrician for physical installation of conduit passage of cables cables, RJ-45 sockets mounted the walls I will. I do not know CAT6 and fiber and in my region has few suppliers.

Questions:

1. Do I really need to use CAT6 or fiber, 10 Gbps Switch?
2. I think about installing a powerful Switch between the two buildings to interconnect them, its correct?

The big reason for using fibre for your buildings will probably be distance, not speed. If the cable runs will be under 100m, CAT5E will work fine for 1gbit, or CAT6a for 10gbit.

Fibre can go for kilometers, if you are willing to pay the premium. It also has the advantage of being more likely to be upgradable without running new cable, just replacing the optics at both ends.

The other reason for fibre is electrically isolating the two buildings. If the buildings have different ground potentials, you can have issues with ethernet. Lightning can also be a concern running cable outdoors. If the buildings are right beside each other, this probably wont be an issue, but it could be.

For where you need switches, and what speeds they need to be, you need to consider the traffic flow between sections. This depends a lot on what people are doing. If a lot of traffic stays local to a floor/department, keeping them all on the same switches means needing less uplink bandwidth.

When you run the cables, dont just run one, at least for relatively cheap ethernet cable. Between the buildings run at least 4 if possible - so you use trunking to combine them for faster speeds between switches, and so you have spares if one breaks. If possible, run the cables in conduit and add pull string to make it easy to add more/upgrade later.