Some Basic Questions from a Newbie

Opencart version : 1.5.6.1

My Opencart store has around 20000 previous orders.
-Should I delete them(previous orders) from time to time ?
-Does not deleting has a negative or positive effect on performance.
-What other data should be cleaned (or needed) to be cleaned from time to time.

And open to your advices to a beginner.What info you knew now , you said wish you knew when started.

Thanks

Basically: the less records, the faster the response time.
On the other hand, if the sever is good enough, a few 100.000 records may result in only a few milliseconds more.

About deleting your order records: don't know from where you are, but as I think, almost every country on this planet as fiscal rules.
And depending on your country, you have to keep an store such records between 7 and 15 years!