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Good additional strategy is to purchase and 301 redirect an expired, aged domain (or several) that already has a few dozen authoritative domains linking to it, preferably a domain with history in the same niche.. this usually results in a nice boost - but it may take several weeks to take affect. Fire a few links at the expired domain to speed up the process.

There's a few ways to look at this.. but it entirely depends on the domains. If they are all brand domains, then you secure your brand names and redirect all traffic to the main domain. If you're aiming at SEO value, then you gain the authority (if there is any) of all the domains that you redirect to the primary.

Why wouldn't you want to redirect 100 domains? Honestly I don't think Google would look at that like a red flag, but again it entirely depends on the domains. If you redirect domains with bad reputation, or former penalties, then you'll automatically inherit the bad reputation. So that can work either way - depends on the domains.