Voting 101: Primary elections are always politically "tactical" meaning you vote for the best person offered by your party. General elections are politically "strategic" meaning you should vote for the main party that most closely supports the trends and directions you want the country to take -period. Nobody expects any party to be 100% right with your ideals, hence "trends and directions." Individual candidates, aren't the winners or losers in general elections, parties are. The winning party gets to set the fiscal and legislative agenda, rule the committees and sub-committees, confirm or reject court appointments, ratify treaties, etc. If your candidate wins, but his party loses, your candidate might as well be on the moon for all the good he'll do you. Remember, primaries are tactical, generals are strategic. And please don't cloud the issue with religious tests- you're not electing a saint - just a politician. His faith is none of your business just as yours is none of his. At election time, put your country ahead of your church. You'll live. And ignore all third parties, thank you. Nobody cares about your petty ideological narcissism and it splits the vote for the party closest to your beliefs, guaranteeing you'll live under the greater of your 2 evils. Like it or not, a vote for the Libertarian is a vote for the Democrat; a vote for the Green is a vote for the Republican. Not voting? Screw you. And I don't want to hear your side of it.
Am I a single issue voter? it depends on how broadly you define the issue. If the issue is large - a socialist vs. a capitalist, yeah I'm a single issue voter. If the issue is narrower, such as social, military, fiscal or foreign policies, it would depend on how far apart the party platforms (not the candidates) were on the issue. If one party is pro-choice, and the other is pro-life but with plenty of exceptions, I would find the difference inconsequential.
Fortunately for my decision-making convenience, one party usually trends in my general direction almost across the issues board. The party platforms are generally 'right' or 'wrong' on numerous issues - rarely on just one or two. So, in the real world, having to make a single issue vote almost never actually comes up.