Should i wait for it to decrease?
You should not wait for it to decrease if you are planning to hold it long term since you will profit anyway. If you would only hold it for months, consider waiting for a dump first.
How long could it be keep increasing in value?
No one can tell you the overall duration of btc price increase but one thing is for sure, it will continue to rise in value so long as there is a growing demand for it.
When is the best time to enter the market for me?
The best time to enter the btc market is when it have dumped hard but finding chances like this is pretty rare so just always have some money ready in case a dump happen. Just buy using 1/4 of your planned investment capital then buy every dip and dump until you have invested all of your capital.