We’ve just sold one of these for around 75% of it’s original retail price after 3 years of good use so don’t be afraid to spend the cash on something good:
http://www.chariotcarriers.com/english/html/cougar.php
For round the farm you can use the full on 3-wheeler jogging kit mode.
For the bike there’s the trailer kit (which works well, it’s not an afterthought by the designers)
For the shops/town/etc there’s the two buggy wheels you replace the jogging wheel with.
All the above can be on the buggy at the same time, so you can cycle somewhere, convert it to 3-wheels for a long walk and then convert to buggy mode to nip into the shop on the way back.
Really well made bit of kit.