Setup/Upgrade Network for 20-30 users at each site with possibility if growth

Hi Ralston18, thanks for responding. This is not a homework, it is real.
For e.: The aim is for upper management guys to be able to call into/or involve in an ongoing video conference from their mobiles or company laptops. We intend to deploy Polycom Video conferencing system in the meeting room, if a meeting is scheduled and someone is on the move, the person should be able to call into the conference room.
I googled and found that Polycom has a web/desktop/mobile app "RealPresence" that "can" do that.

I have been on the Manage side of network infra, this once I have been asked to plan/upgrade an existing network as described above.

I pray you experts to help me check and evaluate what (the solutions) I have listed above.
If I have missed something, please do point it out.

Any suggestions/recommendations/advise are highly appreciated.

Thanks again.

PS: The Admin that setup and managed the network did not leave any notes, this is especially for the VoIP.
The firm has been offline for sometime now.

Suggest Network/Server hardware, services and anything that would enable me to do a good job.

Thank you guys, a lot.

Thanks a lot Ralston18.
For a.: The both sites were never interconnected in the past, now there is a need for site A to speak with Site B and any other future branch. They need to share information in a reliably secured and fast way.
I have also checked, there seam to be more way to get this done; MPLS, VPN and Cloud based WAN. Having gone through some materials online, it appears (to me) that VPN is easier to configure, plus it is also secured and can be done with VPNready routers.

For b.: They have two server hardware (dell poweredge) at both sites, configured as file servers in Workrgoups. No Domain exists. In addition to sharing files easily, they also want to secure those files from unauthorized personnel, hence the AD. The question is now how best to implement this; 1. deploy writable domain controllers to both sites, 2. deploy writable to site A and RODC to site B. That's where the centrally manage came on-board.

For c1.: The are two UC500 VoIP devices, one at each sites. IP phones are working locally, but intersite has not been achieved. I did a little search on google and saw something like Multisite connection or trunking.
Note: no details about the current config, no config record from the previous admin.

For c2.: They want to have a professional email "name@companyname.com. Now I can install and configure a local exchange server, but I haven't done anything like making it reachable from the outside. I've read a few articles, but seems heavy. I found it's possible on Microsoft cloud using office360 or from Godaddy. Actually I found out about Godaddy in this forum.

For d.: Securing the network from outside is as important as securing network resources from within, if not more.
That's where the Firewall comes in and Antivirus to protect from viruses and malware.

Products that I am considering:
Routers: I would go for Cisco, I am not a routing guy, but I can find my way.
Manageable switches: I will go for Cisco. I haven't worked with any other one before. I am comfortable with Cisco
Server Hardware: I have worked with HP products "HP ProLiant Servers DL380 G7/8

Let me know any other info you need.
I need your suggestion, recommendations and advise.

Thanks