I would start by planning your garden, as if it has a structure that is conducive to good growth and is visually appealing you will be less likely to have to make major changes later on.
The fact that you are gardening in a southwest facing garden is a great start, as this will give you plenty of light and warmth - potentially with some microclimates that will be fantastic for more adventurous planting.
Plan a mixture of foliage types and colours - as you want vegetables and ornamentals this immediately gives you some variety. Add a variety of heights too and if possible shield some areas, so not everything is visible in one glance - I realise this is a little more challenging in a smaller plot, but it's still achievable. Make use of climbers on your walls/fences, or construct something for them to grow on and cling to. And have evergreen as well as some deciduous plants, with a goal to have something of interest for every season.
If you have zones then this would allow you to focus on getting certain areas finished, without having to necessarily do everything at once - as you've realised, weeds will move back in again, as their seeds will be around your garden soil. As summer's now pretty much finished you can plan and prepare for next spring's planting for many of the plants such as Tomatoes and Peppers.
Anything that you want grown in a pot - such as your mints, which will contain their spread (many of them can be a little invasive) could be started now too, as these are moveable. It would be fine to take some mint cuttings and get them started now - if you get rooted plants, these can be moved at most times of the year.
Some easy perennial low maintenance plants, that are generally trouble free include hardy geraniums, Hebes, Heucheras: many of these now have incredible foliage colours, such as creme brulee, and tons of them are great in shady spots, if your garden has any, A plant group to consider for late winter/early spring flowering are the Hellebores, including the Christmas Rose or Helleborus niger.
Many bulbs, as you mentioned you wanted to use these, are also easy and low maintenance. I'd aim to get some miniature narcissus, such as Tete a Tete, as these add late winter flower colour too. I have some that have been great in pots for the last 6 years or so, though they're also great in beds.
Thomson and Morgan seeds offer many perennial plant seeds, and you will find many friends and gardeners happily donate cuttings or small plants - this was how I started when I was younger. I still grow most of my plants from cuttings and seeds.
Final thoughts on a good evergreen plant to use is the Phorium group - these come in dwarfer and larger forms, and colours from green, variegated to bronze and reds. They have spear shaped leaves, so you get the variety of the ever-present colour, as well as their more unusual leaf shapes.
Lastly, include some scented plants, as you may as well have the bonus of strong scents, alongside beautiful colour. Honeysuckles and Jasmines are great for scent, and will climb up walls or trellis, making fantastic use of space.
Preparation - deep digging and incorporation of plenty of organic material, such as compost or well rotted animal manure will pay dividends. Doing this, with several months before planting, will allow the material to break down, be moved around by worms etc, and be excellent for plants that are planted spring time. Always use fully rotted manure before plants go in the ground, as this will not affect your plants in anything but a positive way.
The methods for taking cuttings vary according to which plants you're propogating. Some plants are good with small unripe cuttings, others are better with bigger cuttings of semi-ripe plant material. Otherwise many herbaceous plants can be divided when they are at rest, and will already have roots that will allow your new plants to continue to grow. As a beginner, it's wise to check for each plant type that you have the potential to propogate, either by asking friends, or checking on the internet/a book.
I'm always really happy to help with any questions, or if you want to test out any ideas etc.
Hope these quick ideas help. Good luck with your new garden! Rob