New guy got a couple questions

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I recently got a a baby burmese. His name is Diesel, (Snow Dogs not Vin). I have always wanted one and but my ex was terrified. He is very quickly growing in size. Even the pet shop owners, who are very knowledgeable, were surprised at how quick he is growing. No I'm not power feeding. Only 2 mice about every four days. Just whenever he looks hungry.
How long before I should give him some more space?
Can you really tell this young what the sex is?
Live feed or not? I just thump the mice on the back of the head and it works for now.
There is a beautiful 9' female Burm that loves me. I have never owned a Burm before but I have experience with other snakes and reptiles. What do I do? I keep hoping that someone will buy her before I do.
Just to let you know I have handle her several times as well as my 5 and 8 year olds. She is really sweet.
I am just don't know how quickly she will grow from her current size and I don't have anyone else except my kids to help me if needed.
Finally thanks to everyone for any advice in advance. I am really looking forward to this forum.

SOLAMF