Better late than never . Always next year, unless you find an alternative, less stressful method of heating your house.How do you fill to the brim when youre ordering a volume in advance? (asking for a thick friend )
Ps thanks for confirming the 5 weeks late advice
For point 1, you need to know the size of your tank and how much is in there. There should be something on your tank somewhere that tells you what size it is.
Depending on where your tank is, how high up and how daring you feel, you can go old school and dip a stick in. An old garden cane will do the job. See how much is wet, work out how much space you have in the tank. Equally, get an oil tank gauge, we have a Watchman one at work. This will tell you how much is left. Do your calculation and then order as much as you dare. You will only get charged for the amount you actually take, not how much you order. If you think you can fit 1,000 litres in then order 1,000, don't worry. The driver will keep an eye out and if they think it all won't go in they will stop. As you are in an oil area they will inevitably be delivering heating oil to other houses so they should be able to get rid of the excess without issue, or roll it over for their next fill up. Don't take the mickey and over order by a big margin but don't worry about pushing to the limit.