configure FG-71G - need advice for newbie

hi there,

need advice, and some helps for best setup to my needs.

I just bought Fortigate FG-71G.

this fortigate will manage:
- 4 ISP: ISP_1, ISP_2, ISP_3, ISP_4. only ISP_1 and ISP_2 have public IP.

- this fortigate will connect to another fortigate use VPN IPSEC via ISP_1 (backup with ISP_2) if ISP_1 down.
- also will use VPN SSL use connection ISP_1, backup with ISP_2 if ISP_1 down.

- 5 unit floor (each floor can't communicate each others, unless require different, (unit_A to Unit_E) with:
1. unit_A
- don't have access internet
- can communicate with unit_B, with limited services.

2. unit_B
- will have access internet via ISP_4.
- can communicate with unit_A, with limited services.
- if some case ISP_4 down, it may use ISP_3 (configure/ switch manually)

3. unit_C
- will have access internet via ISP_4
- need divide into 3 groups, but can access 1 shared printer.
- each groups can't communicate each other (except to shared printer). shared printer will be connect to Active directory in same network.
- if some case ISP_4 down, it may use ISP_3 (configure/ switch manually)

4. unit_D
- will have access internet via ISP_3
- if some case ISP_4 down, it may use ISP_3 (configure/ switch manually)

5. unit_E
- will have access internet via ISP_1 or ISP_2 (can be auto balance, or fail over).
- need divide into 2 groups.
- if possible, specifically group_1 use ISP_1 , group_2 use ISP_2 (optional).
- each groups can't communicate each other
- all groups can access shared printer on unit_C

is that possible to implement above conditions?

currently I only use unmanaged Switch hub. if there will be need managed switch, please advice layer 2 or need layer 3, and at what point I need to attach.

thank you