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OoOPs! I forgot this is only white-hat forum/QA board. but buying domains in bulk and redirecting to main site is also blackhat. 301 was supposed to be a transfer, If your website is shifted from domainA to domainB then you can redirect 301 from domainA to DomainB. Anyways, Do make a try with your strategy. I've shared what worked for me

Its a good thing, but I'd prefer to use expired domain as a backlink source.
Its called Site-network or Blog-network. Register 10-20 domains with different PR's and DA's. Put high quality content (related to your topic) and then link to your client's website with different anchor tags. then see Boom in rankings! I ranked a 52% Keyword difficulty keyword using this method in 1 month.. Exact!