PBN help

I am creating my OWN PBN. It includes blogger , Wordpress and weebly. but not using TLD.

Is it ok not using TLD?

buy Expired domain is a must or not ?

last ,i need to know that , what is best strategy to make PBN?

The best strategy would be to pay somebody who actually knows how PBNs work, otherwise you will lose time.

I think what you described is considered as Web 2.0 rather than PBN, PBN usually means using TLDs or so I thought. Still works but Web 2.0s like what you're doing are harder to get indexed and they are a subdomain, so you don't get the same authority juice as you would from the main domain which has backlinks to it already. Wordpress works the best but also gets banned the most IMO.

A PBN made up of web2.0 sites can be useful but is unlikely to rival a PBN made up of domains you control entirely. It is easy to build up a bunch of web2.0 accounts and their usefulness will fluctuate whereas a bunch of reasonably strong domains will be an evergreen source of SEO benefit