Limit Orders

I am new to crypto, and am hoping for some guidance and advice from others with more experience.

Should limit orders be set on the dollar such as $5.00 or slightly off, such as $5.03? I've read things about both. Is one more beneficial over the other? Would limit orders get missed if on the dollar?

Also, should you put all of your crypto in limit orders or maybe just 50% or 75% of each coin and hold onto the remainder?

Thirdly, when is best to store on a nano ledger?

Fourthly, USD or USDT??

Any other tips anyone wishes to share would be helpful also.