Ok. The only real mistake is that you can't claim the 8% interest before you file a claim at court and this shouldn't be mentioned in your prelim and LBA.
Sending copies of statements is fine, except that you have to send these several times in the course of your claim. Much better to use a schedule of charges (just a single sheet). Plus the online-calculator is under-calculating at 7.3% instead of 8%
Use the Simple s/s here:
6. Interest calculation spreadsheets
Overwrite the existing example type of charge, amount and date. The days since and 8% will be calculated automatically.
Save it (for use later at court), delete/hide the last 2 columns (8% bits) and print out as your schedule of charges and enclose this with your LBA