1. These organizations will focus on servicing clients with market leader technologies; Adobe, Salesforce, etc. There will be very little if any bespoke work, unless they're lucky to win some creative/communications projects. As such, they tend to attract large clients who can afford such projects — i.e. automotive, financial services and insurance, governments etc.

2. Bonuses maybe, but I've never heard of a commission model in those organizations for developers. Bonuses are usually not paid unless you are at an executive seniority with lead-generation or client-service role (in which case, very likely you are not a day-to-day developer)

3. Travel is very common, even for developers. The more senior you are in your role, the more likely you will travel for pitches and meetings. Developers can be co-located (i.e. you work client-side), and this is common when you have a few local leads and have development teams elsewhere (i.e. India, Poland, etc). You are a 'consultant' first, developer second.

4. Glassdoor/LinkedIn salaries are fairly accurate. From my experience, tech companies will pay more, have greater benefits, and bonuses. Few of these organizations are publicly traded, so there's no shares. However, if you are a specialized talent, i.e. Salesforce architect, Amazon Cloud certification etc., you can expect a significantly higher salary as those roles allow the organizations to go for accreditation and can be billed to clients at a much higher rate. Clients are happy to pay for "Salesforce experts," but will wonder why every other developer isn't 50 EUR an hour...

5. Most consultancies are very heavily invested in the technology space, and I have found that these organizations tend to have very clear performance frameworks for promotion. Largely, however, it focuses on the "client service pathways" i.e. if you want to be promoted, expect to do more and more client service work — pitches, planning, team management, etc. And less development over time.

As for contracting, IR35 has changed the UK landscape a lot. There is a lot of money for specialized talent (experts in a particular product suite), but because of IR35 I feel most organization will try and hire internally to avoid the grind of per-project contracts.

Tax and accounting is easy, a good accountant for c. £100 a month will cover everything for you such as payroll, any accountancy questions and preparing your end of year company tax returns (CT600) as well as your personal self assessment each year. Honestly the most I have to do each month is send an invoice to the client which takes about 10 minutes and tag a couple of business transactions in FreeAgent every couple of weeks.

Keeping a pipeline of work is obviously the trickier part, but once you get your first couple of contracts (probably via a recruitment agent) then you quickly build up a network of other independent contractors you can reach out to as well as any other permanent members of staff you worked well with who have moved to new roles etc.

What relationships? In the UK, most people find contracts on job boards. You just filter by "Contract", instead of "Permanent". After that, there's a job interview etc. The advantage of being a contractor is that the interviews are much more relaxed and there's no HR involved in them at all.