The required configuraiton really depends on your current configuration.
If I were to presume that you have no interface ACLs configured then you will need an ACL configured on the DMZ interface since you need to allow traffic to a higher "security-level" interfaces networks.
Typically connections from DMZ to LAN are not allowed that broadly.
Since you are essentially asking to allow all traffic from DMZ to LAN and also need to allow traffic from DMZ to the external network then you could simply add
access-list DMZ-IN remark Allow all traffic from DMZ
access-list DMZ-IN permit ip
access-group DMZ-IN in interface DMZ
NAT work in Bidirectional mode , e.g
Suppose you are doing Source NAT form Inside to DMZ . So for the trafiic comming from DMZ to Inside it works as Destination NAT.
And if you want to do Source NAT from DMZ to Inside , then u can do this by :
Doing Destination NAT from Inside to DMZ or Source NAT from DMZ to Inside.
Hope this helps you.
You need a static NAT to go from DMZ to inside. Do you want to allow just C1 or the whole subnet that C1 is on ?
If just C1 then using 192.168.5.10 as C1's IP -
static (inside,DMZ) 192.168.5.10 192.168.5.10 netmask 255.255.255.255
if you want to be able access any inside host on the 192.168.5.0/24 network -
static (inside,DMZ) 192.168.5.0 192.168.5.0 netmask 255.255.255.0