write checks to my personal bank account

Here is my situation:

When I started my business in Feb, my business bank account was not ready yet, so I purchased some inventories using my personal bank card. Also, after I had my business bank account, I forgot to bring my bussiness bank card, thus I purchased some inventories again using my personal bank card. Of course I have all the receipts, so I think I should be able to write a check to myself to reimburse these expense, right? Is there any rule to follow? or something I need to pay attention to for this kind of transactions/things?

Also, my primary customers are from USA, so all my incomes are in USD. Currently, CAD is so high, can I write a check to reimburse my expense based on today's exchange rate?

For example,

I purchased $1000 CAD worth of inventory using my personal bank card, I am supposed to write a check (from my business account) to myself (personal account) because this pruchase is for my bussiness, let's say, based on today's exchange rate, 1000CAD = 900USD, so can I write a $900USD check (from my business account) to myself (personal account) to reimburse the $1000 CAD expense?

Not sure if I explained it well, hope you guys understand :-)

Thanks in advance.

Yes you can reimburse yourself for purchases you made personally. For currency conversion, I believe that accountants prefer you to base the conversion rate on the sale date not the current date. (i.e. you bought it on Jan 4 and reimburse on May 30... calculate the currency conversion on Jan 4 exchange rate, not May 30).