1) You make a post, someone quotes that post and gives a reply. Now you delete that post, making it look weird. If everyone starts doing this, we will see chaos here. Also, it is not justified for the members who took time to reply to your queries.
Yes you're right besides that's not help you eve though you deleted post and you're activity will lose if you do that.
Just keep on posting and if you know that was deserving to have smerit and that's okay.
2.) If you delete all merited messages and keep only posts with merits, it will look suspicious.
I did not understand this question why you should delete all merited messages, if your thought that you will delete all unmerit post and remain the post with smerit then yes it might going you to ban i that way. No begging smerit just to earn maybe
3) I know that there is lot of competition for merits but you need not affect your activity for that. If you learn from this and stop posting those meaningless post in future, it is more than sufficient.
Yes just keep on posting in high quality post i think there's maybe a chance to have smerit just relax and take it easy.