I don't think this is an issue of Stockport specifically, but in general of LLM. Don't even bother to do transfers in BSX or BSP. You won't have the funds to buy anyone even remotely useful for your team. You need to rely solely on free transfers. You probably have a salary budget that you can increase, so do that. Take a couple of scouts and search for decent players without contracts and sign them. If you feel like putting in the work, U19 and U21 teams from weak European countries may have some players willing to sign for you. Because they're part of EU, they won't need a work permit even if they're from another country. Otherwise, hire a second scout and him to scout the UK.
I don't know how Stockport plays, but try to identify the strong side of your game (this is where the team report comes in handy). For example, when I started out with Blyth in BSN, I noticed that they play a good passing game and that the team's average passing is among the highest in the league. I also noticed that they were one of the slowest teams in the league. My signings were therefore geared towards two things: maintaining and improving the high passing rating to keep the same style of play going and improving our speed. So try to identify one main strength and one main weakness of your team and sign players to improve on the strength and to fix the weakness. For example, whenever I search for players, I always have a minimum passing ability filter. No matter how good the player, I won't consider them if they can't pass well. The result is that the team continues to play a pretty Spain-esque passing football. Your team may have different strengths. For example it may be good at headers. For that you'll need a good free-kick taker to take advantage of any set pieces and more tall players with good heading, positioning, anticipation, and jumping abilities.
Of course, you can try to change how your team plays entirely, but I personally think that you can't really do that with the budget you're given in the lower leagues.
Also, make sure that when you sign players that they fit your squad mentality. Scouts will usually mention this in their reports. Squad harmony is crucial to teams that are in danger of relegation and thus lose a lot of matches. My Blyth team is composed almost entirely of "balanced" or "loyal" players and they were able to get through really difficult patches without losing morale. On the other hand, I recently made the mistake of purchasing two "ambitious" strikers and they're really making things more difficult for me.
And finally, from what I learned, pace and acceleration are probably the most crucial abilities in the lower leagues. High-paced strikers will score more goals than slower ones, even if their finishing is utter ****. In my Blyth team, I started out with a 5-star striker who was considered "good enough for npower 2" and a 1-star Les Mason with something like 2 finishing and 6 composure, but high speed and acceleration. My 5-star striker managed 5 goals in the whole season and I ended up benching him. My 1-star guy became the top scorer in the league. Yes, he missed a lot of chances, but the sheer amount of chances he created by simply being faster than the opposition defense meant that he scored enough to get me promoted in the first season.
Hope this helps.