In my opinion, it is better to use all potions and bonuses to parameters immediately.
Saving bonuses until some event is a habit from the original game and here it will not give you anything in essence.
1) the cost of training strength/dexterity is always the same and the only limitation is the training limit of the current teacher;
2) training for Skill Points is very expensive and more than half of the parameters are gained through bonuses;
3) further along the story, teachers appear with a higher learning threshold, which will be difficult to achieve without damaging the hero’s other parameters (weapon proficiency, health, special skills, and so on);
4) a one-time increase, for example, 50 strength, after a total saving of bonuses for the first 2 chapters - will not give a special advantage over enemies, since they will still kill the hero in 2-3 hits and since it is more profitable to increase damage due to special skills and special weapons (with pure damage);
plus the player will suffer during the first 2 chapters due to his saving of bonuses, having difficulty gaining parameters for weapons, running away from enemies and being forced to use abuses - this will not add interest to the game;
5) further along the story there will be more powerful weapons, more powerful equipment and cooler skills, with which killing enemies will be much easier and faster;
6) it is not a particular problem or difficulty to clear the Valley of Mines and Khorinis already in the 2nd chapter (I do not use the bonus saving) - the modification has everything necessary for this, but it will require careful exploration of the world and selection of the right weapons/equipment/skills.
Something like that.