The 'sc' and 'score' commands give alot of information about your stats, etc. But the information regarding "encumberance" is minimal. In the nanny help info, STR is defined as "affects your carrying capacity".
Is there any command which will give info on this 'capacity'? such as current/max, etc
You should have your current STR in your score I guess, not sure about all guilds though... The max is at 20, as is the DEX max (CON and INT can be higher for paragons). The encumbrance message just indicates if you carry just a little, or half, or even exactly what you can manage to carry with your current strength (or somewhere in between).