Is there any article published on how to understand army regimental Muster Rolls and Pay-Lists of the Napoleonic era in WO12 at The National Archives, Kew?

I have searched militia and regular regiment/battalion lists from about 1797 to 1815. The format changes over time, but there are certain abbreviations and expressions that are not always clear. I have included a number of questions below, the answers to which may assist others trying to understand pay lists and musters at Kew including the copies online at Ancestry (selected 1812-17).

1. A militia man in 1804 has the word 'Command' in the remarks column of a pay list along with a few others, but all men listed seem to be getting paid a shilling a day. A later regular army soldier in 1810 has the comment 'On comd' at another place from where the regiment was stationed, but the pay list does not include pay for the days he was away 'on command'. What does 'On command' mean?

2. In some militia pay lists against some men in the remarks column is "On Duty", whilst for most men the column is blank, although all men are getting paid a shilling a day. What does "On Duty" mean in that context?

3. Sometimes it is noted that certain Route numbers were taken when men were 'on march'. What are these - were they recorded somewhere in the records?

4. I have seen in the remarks column 'On Pass' or 'on Furlough' which seems fairly self explanatory but did militia/regular private rank soldiers get any leave? For example, I have a man whose wife gave birth in 1804 and he is recorded as being the father at the baptism but he was in the muster stationed 50 miles away (although he did go on a march in that month - could he have dropped in to see her!!?).

5. From June 1810 to end of 1813 that I searched to privates in a regiment stationed overseas was only getting 6d per day? Any reason for this half pay?

6. There is a column on some pay lists (e.g. 1809) which relates to number of days and is headed 'Increased rates to Innkeepers & c' and includes a sub-column 'In lieu of beer'! Not sure what that is all about!

7. In some later pay lists (e.g. 1813) the second column is titled ‘No. of the Report or other Voucher referred to’. The column is usually blank but sometimes there is a number in there for a soldier e.g. '12'. If one is lucky sometimes there is a list of these reports or vouchers at the end of the pay list which may give a brief description such as Report on Invalids sent to hospital' (the number 12 is listed against a number of men whom in the remarks column have been sent to hospital). Would the actual reports survive in other records at Kew?

Ok, I know that is plenty of questions to ask, but as I said any answers may be of interest to quite a few people.
Thanks very much!