Looking good! I'd recommend trying shellac for your first few sealing coats. Evaporative finishes like shellac and lacquer typically adhere better to extractive-rich woods than reactive finishes like varnish. The advantage of using shellac for your sealing coat is dry time minutes at the longest. Also, because shellac is compatible with nearly all finishes, after a couple of thin coats you will be able to build a film with whatever finish you like. You could in fact build a finish using only shellac (I often do), but as it contains no UV inhibitors, you may want to continue using spar varnish for your top coat on exotics like ironwood and cocobolo.