Importing Bills feature is used by Clear Books users to import bills raised in a different system and also while importing historic data. Hence there has to be a wide margin of bill numbering and formats. To answer your questions in the same order,
On import, the Bill number has to be specified since system needs a reference when posting it. Clear Books requires unique reference.
Users may be downloading from a different software and uploading into Clear Books, one does not know what the bill number format would be.
To import multi-currency invoices, Line Net price should be your base currency price in this case say GBP, Line VAT rate will be the VAT rate that you want to use and the multi currency net price and multi currency VAT should be in the currency you need to import ie USD values. See below a sample.
Example upload: Base currency GBP and importing USD invoices
You need all the information below in a columnar form as a csv and the map them to the table once you import the csv
Invoice number : 123PRF
Invoice Date : 14/10/2015
Customer Name : Jo Bloggs
Line description : Cost of licenses
Line Account Code : 1234
Line Quantity : 1
Line net Price 500.00 (GBP)
Line VAT Amt 100.00
Line VAT rate 20%
Currency Code USD
Multi Currency net price 762.66
Multi Currency VAT amount 152.53
4.VAT rate can be specified but if you import VAT amount and rate, amount would supersede the rate. Hence best to import the net amount and the VAT rate allowing the system to post the VAT. Creating invoices in Draft is not possible but on import you can check if you need to post and delete before posting.
Caution: Always take a full back up of the data before you upload any invoices since one posted, there is no way of mass deletion of imported data.
Hope this has been helpful.