HFT is perspective imo. Yes, if you want to be like the medallion fund, thats HFT at a nanosecond level.
But HFT can be achieved I think most effectively using a concept called Fair Value, and gaps in them.
A concept I believe to be initially coined by ICT, a gap in fair value is when a candle produces a sharp move up or down, resulting in the next printed candles low or high to leave nothing but body between the 2 candles.
Logically, a fair value gap up (upgap?) would be C1 low above C3 high, and gapdown would be C1 high below C3 low. When a FVG is initially formed, it would be in the shape of C0 opening higher or lower than C2 high or low....but only the most nimble should play with anything other than a confirmed concept.
picture for support

I might recommend just coding the concept first, make it variable as to time frame, so you can see how the lines are drawn, and then watch a 1 minute perspective while it draws the gaps on a hourly TF, for example...how it creates them, how it fills them...how it rejects them.
logically you will want to use the high and low of each object too, so try to do it as gapuphigh gapuplow, gapdownhigh, gapdownlow, as 4 lines and youll be able to use them that way.
As in all things EA (trading), money management is the most important. Id likely believe that RR for HFT should be the goal, because entries are least important. You must manage the financial risk heavily first with a smart MM strategy. You wont make it long enough to trade frequently if that isnt proven first.....Aggressive stop movement, profit target that will overcome losses, RR for repeatable proven performance, and how do you leave some to run.