About to try FIRE at 38. Is this viable?

Hi, long time lurker but finally signed up ;)

• mortgage £270k (overpaid max 10% recently) Value ~£550k
• mortgage offset account cash £250k
• Vanguard lifestrategy 100 s&s isa - £40k
• nutmeg s&s isa - £25k
• pension - £80k
• cash - £150k

The mortgage is almost fully offset, but am only offsetting 2% so could put this money to better use. There is something to be said for having the mortgage paid off, and it is a great feeling that has really changed the way I think about finances and pushed me down the FIRE path. And whatever happens with the markets, economy, Government, tax etc they can't take the roof over your head!

Nutmeg is giving me ~10%, Lifestrategy (80 & 100) is doing much better currently but assuming similar 10% returns the ISAs could be bringing in £6-7k per annum tax free.

I'm 38 so can't touch the pension for another 17 years, which is frustrating as that still feels like a really long time away, but it is doing pretty well currently.

My aim was to pay off the mortgage completely next year once the staggered ERC goes, and to get to £100k ISAs which I can hit in April 2018.

I've came to a figure of £25k for a FIRE salary, which is ~£1700 net per month so a 10% return on the above ISAs goes a long way to covering that.

I'm sat on a higher than usual amount of cash due to a sale of a business, and thought it would be interesting to see what you would suggest in my position.

Would also appreciate any feedback on the salary, it seems low but I've checked my budgets and once the mortgage is gone the next biggest is eating out - which I can definitely do more/less of depending upon returns ;) We have no other debts currently, and the car is paid for (totally inefficient and depreciating, but YOLO)

Thoughts:

• Mine & Wife's ISA maxed out this year.
• Will unlikely be earning anything substantial (if at all) for a year or two so won't get any boost on pension contributions.
• Considering an investment account with the likes of Charles Stanley, and investing further in Vanguard funds. Make use of £11k tax free allowance of CGT?
• Property. A large proportion of net worth is already in main house, and not interested in a rental at the moment.

The investment account seems appealing, and could gradually transfer that into ISAs over the next few years.

If the pension does 5% YOY it will be approaching a £200k pot, which should definitely provide a good bridge of income/draw down until state pension age.

I am considering just spending the cash, £150k is £10k for 15 years that combined with decent ISA returns brings me closer to a FIRE salary. I get most people wouldn't recommend this, and 7% return on that lump sum would do the same thing but investing in funds/stocks clearly has some risk, and if the markets do drop and I have to sit out the long term I feel I'd be forced back to work, whereas just spending it doesn't have that/(any?) risk (could tie up proportions in something safer to beat inflation)

There is obviously the possibility of going back to work part time, consulting or doing something else in a few years should all of the above fail miserably. Hopefully that won't be the case.

Comments, flaws and feedback appreciated!