I think the Vajrayana and Teravadan perspectives can work nicely together, so long as you can just digest and basically ignore the propaganda you will hear about the "Hinayana" from the Tibetans, who basically know nothing about the modern Theravada as it is in places like Burma, so they are talking about some ancient, somewhat anti-idealized creation of their own historical minds, using it basically as a literary or teaching device, a foil. The Theravadans know nearly nothing about the Vajrayana most of the time, but wouldn't even bother to mention them, as it generally has nothing to do with their worldview at all. In summary, we have the Vajrayana using the Theravada as a whipping boy with inaccurate negative propaganda, and the Theravada basically totally ignoring the Vajrayana. I am not sure which is worse, but neither is particularly helpful.
From the Theravada you will get very good technique in great abundance and an extremely practical, practice-based approach. It will give you the sort of foundation that the Tibetan practitioners often lack, whose world often has so much ritual, ornament, cults-of-personality, political and dogmatic stuff that they generally are not doing what the Theravadans do, meaning just busting it on the cushion hour after hour after hour building the muscles you need to perceive things clearly and stabilize attention.
That said, the Theravada has its shadow sides, and from the Vajrayana you gain a perspective that can work with energies, colors, qualities, the textures of space, emotions, the archetypes, and things like that, in a way that is generally more whole, human, vibrant, and immediate than the Theravada often produces, though on paper it involves working with all of that also, in some relatively dry way that often, due to its particular models and some of its dogma, means subtle or overt denial and asceticism beyond what is needed to get really fluent in your reality as it is.
I would seriously consider starting Theravada, getting stream entry and perhaps second path from the Mahasi kids first and then a good sense of what really strong concentration is from the Pau Auk kids, and then take that into the Vajrayana, and you will already have what you need to visualize really well as well as having established a direct understanding of ultimate bodhichitta, which is essential to that path, and be able to see that the endless fascination with ritual and the rest of the hyper-abundant trappings and politics and personality stuff may, at best, be skillful means, as Attachment to Rites and Rituals will be profoundly lessened if not eliminated, and so you will be able to have the wide, vibrant acceptance that the Vajrayana offers without its obvious initial traps that so confuse most people who get into it before they were really ready for it. Dzogchen and its related perspectives really help with 3rd path territory.
My 2ยข,
Daniel
