You are basically done on FTDNA with one exception, BIG-Y but this is new and I am sure the price of $575.00 will come down. You certainly would be an early adopter.
Your initial post did not exactly state your objectives. The primary objective of DNA testing on Wikitree is to compare KNOWN familial connections to see if those comparisons are consistent or inconsistent with the existing tree.
I purchased and manage kits on 23andme, AncestryDNA, and FTDNA of known family members which validated most of my tree. One of those kits discovered a non-paternal event on my male line. It was the evidence needed to refute my claim to a common ancestor and helped another support his claim to that same common ancestor.
Autosomal data is significantly better at providing evidence to support or refute closer relationships. This would be the foundation for your tree, which is why many people are anxious about taking these tests. The risk learning something they wished they didn't know. I can validate that ignorance is true bliss and sometimes preferable.
If validating the foundation of your tree first make sense, then I would test at least one 1st cousin/aunt/uncle on each side of the family, followed by 2nd cousins, etc.
You can't validate or refute anything unless you can find a known DNA cousin to compare. the pool of possible autosomal DNA cousins is significantly greater than the pool of yDNA or mtDNA cousins.
If I were to spend $700 to get started, I would buy 7 autosomal kits and test myself and six of my 1st, 2nd, and/or 3rd cousins.