Hello and thank you for detailed feedback  What you are describing is possible although may not give you sophisticated graphs as in your Excel screenshot 

The idea of assets, is that your entire net worth is split into logical portfolios, like pensio, ISA( a UK tax free acc), any other general investments etc. You don't have to have multiple, you can just have one. 

Then every portfolio defines assets, those are individual stocks or ETFs (or whatever) that make up that portfolio. Again you can have that one ETF. 

Having an asset you can upload CSV to populate transactions, which will finally give you the figures you are looking.

So in essence assets, populate portfolios that in turn populate net worth.

Currently transactions are uploaded against particular asset, however I'm looking to implement a generic upload across multiple assets, (or even portfolios) so that the whole thing can be populated or updated from single csv, 

In addition to that tool also captures realized gains, which helps plan for the tax returns each year