Heya. I'm currently doing the SQE with BPP (also firm sponsored), I passed SQE 1 in first quintile on the first sit and currently doing SQE 2. I was also out of uni for about 5 years before I started the SQE so I believe I can offer some advice
I honestly didn't actually start studying for the SQE until about a week before the course actually started, mainly because they didn't give us access to the materials any earlier. I'm not sure which law schools you're with but you may find that to be the case too. That being said I did believe the 4 months I had to prepare for SQE 1 whilst studying full time was sufficient. I started in mid-Sept and by the time mocks rolled around in mid December I had covered basically 90% of the course content, which left me with roughly over a month for revision before the exams in late January.
My undergrad law knowledge was extremely rusty so needless to say I did have to re-learn everything, but I was surprised by how quickly things came back to me once I started. But the SQE does not examine it in the same way, so like with contract and tort for example, you would have had a full year to learn this as an undergraduate but on the SQE you can learn it in a matter of days because you don't delve into any case law or academic debate, you are only learning the bare principles.
I didn't find it too much of a struggle to get back into studying, the main thing is to treat it like a full time job and be consistent - I was working consistently 5 days a week, several hours a day from the day I started the course, and by the time it was exam season I was studying basically every day. I made sure I prepped for every class and kept up with the workload - because there is so much content to cover, if you slack it is very easy to fall behind, and if you fall behind too much you will struggle to catch up.
Everybody has different study methods, some of my friends favoured flashcards, me personally I didn't use many flashcards and I personally find the volume of information was too unwieldy for flashcards - I favoured mindmaps, writing up notes (both on the computer and by hand) and doing plenty of practice tests to consolidate the knowledge.
The key thing is to make sure you cover everything that is listed on the SQE specification. This is ultimately an exam that favours breadth over depth, don't neglect your undergrad law subjects as they are tested equally to the practical subjects. And do plenty of practice tests to get your technique down. Ultimately the majority of my cohort passed for SQE 1, so it is hard, but doable!