Nobody can forecast how much bitcoin will cost in the near future. I believe you should be the one to decide when to buy in bitcoin because you are expected to know the best moment to invest in bitcoin as a bitcoin investor.Because you intend to invest for a long time, the price of bitcoin should not bother you because even if the price drops while you've put your money in, it won't be your problem because you intend to live there for a long time. If I were to invest now, I would do so since we still believe the price will rise higher than it is presently.
True, long term investors are not worried about current prices to get into still they should not buy at the all time high, to maximize their profit they should do so at the low or middle. We know one thing that Bitcoin will cross it's all time high sooner or later but when we have to wait for that.
The good thing is that you can just keep buying at every low and sleep ok that for years. Sell at a high and then recycle the money. Of course it is a long term and painful process and it will not make you rich overnight.