All required tasks can be accomplished using Mikrotik. Thats the beauty of ROS that its multi tasking system 
1- Single NAT/ROUTE rule will do all the masquerading for local users pointing to your A.A.A.225
2- You can mark all traffic for port 25 (or others required) and then create a rotue which will route all marked traffic for smtp to B.B.B.3
Example:
http://wiki.mikrotik.com/wiki/Per-Traffic_Load_Balancing
OR you can use policy base routing to route specific user/server to force them to route through desired gateway.
http://aacable.wordpress.com/2011/10/27/mikrotik-policy-routing-based-on-client-ip-address/
3- Remote access for what? mikrotik itself like winbox access? or remote to RDP for local pc/server,
if , its winbox, then you actually dont have to create any special rule (unless you are using tight firewall to secure your router then you have to create a rule which will allow inbound access to winbox port) or if you want to route rdp request to local internal pc, then you can use simply port forwarding.
http://aacable.wordpress.com/2013/11/13/mikrotik-with-multiple-wan-ips-and-port-forwarding/
4- Explain ‘illicit’ web sites. If you mean Pornographic sort of sites, then unfortunately mikrotik dont have ‘porn’ filter capability, actually the job of proxy with proper filtering addons , but as a workaround you can use free OPENDNS to filter porn/illegal web sites (categories are selectable). I am using this trick in my company’s TMG from past 2 years with a GREAT success.
http://aacable.wordpress.com/2012/11/22/howto-block-adult-websites-using-opendns-for-free/
5- Yes P2P’s can be blocked using Filter/L7 marking.
http://forum.mikrotik.com/t/block-torrents-p2p-traffic-100-working-on-all-versions/54137/1
http://aacable.wordpress.com/2011/08/15/mikrotik-howto-prevent-mt-host-from-invalid-login-attempts-from-lanwan-users/
As you can see every thing is possible, but UNFORTUNATELY there is no single guide you can follow to create all rules. You have to read several guides. Mikrotik WIKI is one good sort of ‘Howto use Mikrotik, or MIKROTIK EXPLAIN’ book to build good base, but even then you have to consult with forums to build your own customized solution, like one you are searching for.
I have provided you some links to take a good start with, which will surely cover most of the things you are looking for. Also following book will help you to take a good flight with ROS.
http://learnmikrotik.com/index.php?option=com_content&view=article&id=151
Hope this helps.