Tax strategy for maximising self-employed income long-term?

Cottage_Economy

I'm employed and do some freelance web content writing work in my spare time. Have done now for a few years, and employer is fine with it. I don't do anymore than about £6k gross, have almost no expenses and pay a flat rate in tax. I'm thinking there might be a better more advantageous way of using this extra money in the long run to save tax and increase our retirement income.

At the moment we're updating the house as well using some of the extra money to rebuild and restore a few wrecked classic fibreglass cars here and there to have some fun with. Hubby is a massive fan of a particular make of 50s and 60s kit car and seems intent on collecting every model(!) some of which we have rebuilt are relatively valuable and others are increasing as the years go by.

I have a pension scheme at work which I started two years ago at 37. I had never had a pension before. Hubby, 52, has an occupational pension with Royal Mail going on 18 years so far. Before this he had nothing. We have no kid and no plans to, and a reasonable amount of disposable income. We're both basic rate tax payers.

To save tax which could help increase our retirement income in the long-run, would it be better to use the freelance money for a pension? Or keep on making sensible updates to our property, maybe move up the property ladder, and stash money in the cars as collectibles that could be sold to provide an income later in life.

Or maybe use the money to build a bigger business? I'm not really a natural business owner - I have the freelance mentality and kind of like the freedom of it, although have considered suggesting some kind of performance-based venture with one of my clients. He runs a lead generation company so I would write only for a percentage of the money he brings in on the back of what I write, rather than by article as I do at the moment.

Apologies if my questions are simplistic (and the post too long). I'm right at the start of questioning what we're doing and why, and trying to build my knowledge.