The tutorial has no time limit, so you can hire A.I.M. mercs to train your I.M.P. merc right after taking the first sector.

If you have the Forgiving Mode active which generates some income start with Wolf as he has a perk that reduces opertion time by 33% and a trait that reduces train operation time by another 10%, which speeds up your initial training.

Dump on you I.M.P. merc stats like HP, STR, MRK and MEC that Wolf can train.

Then start training with Wolf on your stats until the learn rate starts to slow down.

You can train your stats up to 91 points. So hire next:
* Steroid for HP and STR
* Mouse for AGI and DEX
* Livewire for MEC (only 85, you need Vicki for 91 but she didn't want to work for me yet)
* Barry for EXP
* Raven for MRK
* Raider for LDR
* Dr. Q for MED (only 88)

You end up with most stats at 91:

This is compatible with a Dynamic Duo playthrough if you wait with hiring the next merc until your current trainer has left. After taking the Tutorial village you can buy A.I.M. Gold membership and hire one of the legendary mercs as you Dynamic Duo partner.

Without Forgiving Mode focus on the cheap recruits like Barry, Grizzly, MD, Livewire and Mouse as trainer. The starting money should still give you a few weeks/months of training for your own merc. Try to dump MEC, EXP and MED as these can be lowered to zero which speeds up learning overall.

I tried to do it without Forgving Mode. With the starting money and the money you get in the first sector you can do:
* start with 85 in all stats except 40 in STR and 0 in EXP, MEC and MED
* train with Barry (2 weeks), 4940$, 0 EXP -> 44 EXP
* train with Barry (2 weeks), 4940$, 44 EXP -> 62 EXP
* train with MD (2 weeks), 5630$+900$, 0 MED -> 54 MED
* train with Livewire (2 weeks) 5780$+1100$, 0 MEC -> 41 MEC
* train with Livewire (2 weeks) 5780$, 41 MEC -> 59 MEC
* train with Grizzly (2 weeks), 5040$, 40 STR -> 58 STR
* train with Grizzly (2 weeks), 5040$, 58 STR -> 72 STR

After taking the tutorial village with your merc you get 30.000$ which you can use for more trainings or hiring your desired mercs.