The finger joint may not be that easy to the inexperienced beside's being a very intimadating set up (loud & dangerous & can give a hell of a kick back) it must be done correctly to be safe. A decent bit plus the cost of the wood may be pricey......just my 50 year experienced opinion.....but there will be 50 other opinions also. Does it really have to be finger jointed......doweled is also a good joint selection this wood does nothing at all to require strucual integrity, doesnt move or require lateral support it merely is a spacer & holds weight its bolted in position & will not ever move again im milling my own & have the finger joint bits but will do dowels instead ( using tightbond 11 glue)......finger joint is overkill.
Selection of wood. the density of ash 37.4 lb/cu. ft., red oak is 39.3 lbs/cu. ft., white oak 42.4 lbs cu/ft. so if the weight/density of these species means anything here.....weight bearing/support is the answer.....it makes sense to use white oak opposed to say sugar pine that will rot/compress @ 23.7 lbs/cu ft. Also, if my memory serves me correctly HARD/rock maple was 46 lbs/cu.ft=better than white oak but over kill again for the weight it will be bearing, anyway, i wouldnt use any species unless cabinet grade 6-8% moisture content. In another thread? somone made the comment concerning 1/16"-1/8" in thickness will throw off aligning the front end sheetmetal considerably & the shrinkage that wood has between green/air dried and kiln dried cabinet grade is a considerable difference to do exactly that.
If you are anal about any of your work id apply 6 - 8 coats of marine varnish, polyurathane or even automotive urathane, yes automotive, i did a whole wood bed in it looked great for the 3 years i owned it it has the best UV protectent, good luck to all