Not sure that you really need me to fling my oar in but I will anyway.
PS My background is in accountancy - I wouldn't use excel anymore for fixed asset registers. In the long term you will get much more out of access.
Writing bespoke functions is similar whether you are in Access or Excel you need to just get round the idea of substitute fields variables for cell references and then proceed in a similar fashion while taking into account the idea of lines of unique records rather than unique cells.
Also as Rainlover says I would recommend you start defining the tables in Access and drawing the references between them. You will quickly see that some of your problems don't exist and you'll have a whole load that you hadn't thought about.!!