I think this really depends on who the statistics are aimed at. If it is only for your personal use then the definitions and structures are not so important and do not necessarily have to meet generally-accepted market standards - as long as you understand yourself what they mean.
If the withdrawals do not eat into your initial capital to the extent that it starts to reduce your position sizes then I think you only need a basic excel type spreadsheet that breaks down your various transactions into their various categories and treat them separately in the final analysis. i.e. initial capital plus gains/losses does not have to equal your current capital.
By way of example, here are two extracts from my own Excel workbook:
I’ve made up some figures here for illustration using your 25000 starting capital. So I have one column for the monthly end results and others for the monthly P/L% of capital and cumulative P/L% of capital (blue rings). These are unaffected by deposits and/or withdrawls.
Then comes deposits and withdrawals with separate cumulative figures and the last column is the current balance including P/L, deposits and withdrawals.
These various columns are then automatically transferred to another table which I call my equity analysis:
Here are separately listed initial capital/deposits/drawings/P/L YTD/ % YTD and current balance.
This is very basic but good enough for my purposes to track my progress. At the end of month it is easy to transfer the data to my official business accounts.
I do also keep separate data for various categories of trades i.e. Forex/Commodities/Indices and these could also be listed separately if desired in the summary table.
This is very basic and only good for personal use and can be reduced/expanded as required.
But if the aim is to build results data for future possible use in, for example, managed accounts, then I guess this is far from the right vehicle.
The issue does start to get more difficult, as you say, once you start to change the “initial capital” on which both position size and results analysis are based.
But I have written enough here for now, I am sure there are others here with much better input to this kind of issue. So this is just a prompter for more input from the experts!