Bid or close price for expert advisor

Hi everyone,
I’ve started to develop an EA, and I’m not sure what price I should use.

The strategy in my EA is based on a predictive algorithm, now, I trained the algorithm with historical bid closing prices for the EUR/USD pair (not so easy to find reliable historical data).

The logic in the EA is roughly this:
1 - collect n number of prices (should I use Bid or Open[0]?)
2 - make a prediction
3 - open an order

Having trained the algorithm with the closing bid price, I’d suppose I should use the bid price, the one that is in the variable Bid not the one that’s stored in Close[0].

Question n 1
What price is correct to use?

Question n 2
If I use the bid price (i.e. Bid object) and predict that the bid price is going up is it correct if I open a buy order based on that prediction?

Thank you so much.

I’m pretty new to forex.

Best of luck with your trades.

Luca