Second property mortgage with help-to-buy

Gg1295

Hi all,
Firstly, thank you for taking the time to read this. Appreciate the below is a bit of a brain spill!

I am currently awaiting a meeting with a broker, however, before getting carried away I thought it'd be best to discuss here to see if my plan is viable. 

My partner and I are looking at getting our first place together, and given the recent SDT levy, it seemed like a good time to start looking.

I already own a residential mortgage under my name and am locked into a 5yr fixed mortgage with a help to buy equity loan of 20%.

Having just come into some money, my thinking is that I could transfer my current mortgage to a buy-to-let product and benefit from rental income, whilst waitOMG for the flat to appreciate (new build) before I sell it. 

The complications I have ran into are the following:
1. under the conditions of the HTB government equity loan, I am unable to 'sub-let' my flat and would have to repay the loan back before I can switch to a buy-to-let.
2. I am still 2 years into my fixed year term on my current mortgage (potential ERC's)

RE point number 1, my question is... 
- Can I work with a broker to switch my product to a buy-to-let, and in the process release equity to pay of my help-to-buy loan? (+ potentially bolster our deposit for the mortgage)
- would I be able to apply for a residential mortgage with my partner without them (the lender) considering my current residential mortgage loan?

RE point number 2, my question is...
- I have been advised by Accord Mortgages that if I stay with the same lender that I would not incur an early repayment charge as I would be staying with the same lender. However, this was based on a general mortgage assumption... would the help-to-buy conditions complicate this at all?

Many thanks!!! appreciate any advice at all.
Greg