It would be great, if it were possible to set hourly rates for certain tasks depending on the customer. better than having to create the same task over and over for each customer and add the customer name or code to the task name.

Необходимо добавить интерфейс частичной оплаты счёта. А то сейчас приходится в эксельке вести всё. Очень часто выставляю счёт клиенту, а клиент погашает счета в 2-3 этапа.

The current system of recalculating the rate doesn't allow the discount to be visible to the client.
It's important for the client to see your full rate and what you are worth and then the discount as a percent, amount and description that can be entered under each costing item separately and subtracted from each item before the total.

Then to also track discounts per service/time would also be possible.

I can't see those explained in the FAQ... I live in The Netherlands, so we use Euro as currency and have 4 different kinds of VAT rules (6%, 21%, 0% and something resembling "VAT by other party"). Pack that with a dutch translation and I think you've got yourself another market...

I'd love to set my own a default message and email subject line to appear in the box that pops up when I send the bill to my clients

It would be great if we can add the code number of our customers to the number format of our bills.

For example: {customerCode}/{year}-{number}

Or even better: Introduce a customer ID/number :-)
{customerID}/{year}-{number}